diff --git a/parameters/extensions.py b/parameters/extensions.py
index dddbe42..666bc3f 100644
--- a/parameters/extensions.py
+++ b/parameters/extensions.py
@@ -35,6 +35,15 @@
 input/SBBX.xxxx is used (case insensitive search).
 """
 
+element = ''
+"""
+Which meteorological element is analysed when a (GHCN-M v3
+format) data file contains more than one.
+
+When using ISTI files, set this to "TAVG", "TMIN", "TMAX" as
+appropriate.
+"""
+
 augment_metadata = ''
 """
 (In the usual analysis this parameter is empty) This parameter enables
diff --git a/tool/gio.py b/tool/gio.py
index 77c0a87..8734fe9 100644
--- a/tool/gio.py
+++ b/tool/gio.py
@@ -428,7 +428,8 @@ def write(self, record):
     def close(self):
         self.f.close()
 
-def GHCNV3Reader(path=None, file=None, meta=None, year_min=None, scale=None):
+def GHCNV3Reader(path=None, file=None, meta=None,
+  year_min=None, scale=None, element=None):
     """Reads a file in GHCN V3 .dat format and yields each station
     record (as a giss_data.Series instance).  For now, this treats
     all the data for a station as a single record (contrast with GHCN V2
@@ -447,6 +448,16 @@ def GHCNV3Reader(path=None, file=None, meta=None, year_min=None, scale=None):
     specified in the file (normally for monthly means this is "TAVG" and
     the scale implied by that is 0.01 (degrees C)).
 
+    The default behaviour for *element* (when None) is to assume
+    that the input file contains exactly one sort of element and the
+    values for this element are returned. In the usual analysis this
+    is a GHCN-M v3 file containing TAVG. If the input file
+    contains more than one sort of element (such as an ISTI
+    file) then an exception will be raised. In order to read
+    from a file containing more than one sort of element,
+    specify the element with this argument. For example,
+    element='TMIN'.
+
     See ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/README for format
     of this file.
     """
@@ -516,12 +527,14 @@ def convert(s):
         record = code.giss_data.Series(**key)
         for line in lines:
             year = int(line[11:15])
-            element = line[15:19]
-            note_element(element)
+            found_element = line[15:19]
+            if element and element != found_element:
+                continue
+            note_element(found_element)
             if scale:
                 multiplier = scale
             else:
-                multiplier = element_scale[element]
+                multiplier = element_scale[found_element]
             values = [convert(line[i:i+8]) for i in range(19,115,8)]
             if values != all_missing:
                 record.add_year(year, values)
@@ -999,11 +1012,12 @@ def read_USHCN_stations(ushcn_v1_station_path, ushcn_v2_station_path):
     return stations
 
 
-def station_metadata(path=None, file=None, format='v3'):
+def station_metadata(path=None, file=None, format='giss_v3'):
     """Read station metadata from file, return it as a dictionary.
     *format* specifies the format of the metadata can be:
     'v2' for GHCN v2 (with some GISTEMP modifications);
-    'v3' for GHCN v3 (with some GISTEMP modifications);
+    'giss_v3' for GHCN v3 (with some GISTEMP modifications);
+    'v3' for GHCN v3 (with some blank field variations allowed);
     'ushcnv2' for USHCN v2.
 
     GHCN v2
@@ -1067,7 +1081,7 @@ def station_metadata(path=None, file=None, format='v3'):
     # Do not supply both arguments!
     assert not (file and path)
 
-    assert format in ('v2', 'v3', 'ushcnv2')
+    assert format in ('giss_v3', 'v2', 'v3', 'ushcnv2')
     if path:
         try:
             file = open(path)
@@ -1077,14 +1091,17 @@ def station_metadata(path=None, file=None, format='v3'):
             return {}
     assert file
 
-    # With the beta GHCN V3 metadata, several fields are blank for some
-    # stations.  When processed as ints, these will get converted to
-    # None."""
+    # In order to process metadata which is nearly in GHCN-M v3
+    # format (such as metadata GHCN-M v3 beta, or from ISTI, or
+    # from github.com/drj11/scar) we allow the derived metadata
+    # fields (grelev, popsiz, and so on) to be blank or absent.
+    # When processed as ints, these will get converted to None.
     def blank_int(s):
-        """Convert a field to an int, or if it is blank, convert to
-        None."""
+        """
+        Convert a field to int, or if it is blank, convert to None.
+        """
 
-        if s.isspace():
+        if s == '' or s.isspace():
             return None
         return int(s)
 
@@ -1179,10 +1196,12 @@ def blank_int(s):
         name=    (36,66, str),
     )
         
-    if 'v2' == format:
+    if 'giss_v3' == format:
+        fields = v3fields
+    elif 'v2' == format:
         fields = v2fields
     elif 'v3' == format:
-        fields = v3fields
+        fields = v3_ghcn_fields
     elif 'ushcnv2' == format:
         fields = ushcnv2fields
 
@@ -1248,7 +1267,32 @@ def read_hohenpeissenberg(path, meta=None, year_min=None):
             record.add_year(year, temps)
     yield record
 
-def read_generic(name):
+def read_generic_v3(name):
+    """
+    Reads a "generic" source in GHCN-M v3 format.
+
+    *name* should be the name of the .dat file, in the input/
+    directory.  The .inv file found alongside will be used for
+    metadata.
+    """
+
+    filename = os.path.join("input", name)
+    if not name.endswith('.dat'):
+        raise Exception("Don't know where to look for .inv file for GHCN-M v2 format file: %r" % name)
+
+    if parameters.element:
+        element = parameters.element
+    else:
+        element = None
+
+    invfile = name[:-4] + '.inv'
+    invfile = os.path.join("input", invfile)
+    return GHCNV3Reader(file=open(filename),
+      meta=augmented_station_metadata(invfile, format='v3'),
+      year_min=code.giss_data.BASE_YEAR,
+      element=element)
+
+def read_generic_v2(name):
     """Reads a "generic" source.  *name* should be a prefix, generally
     ending in '.v2', example: "ca.v2".  In the input directory the data
     file "foo.v2.mean" will be opened (where *name* is "foo.v2") and
@@ -1347,7 +1391,7 @@ def v3meta():
 
     v3inv = os.path.join('input', 'v3.inv')
     if not _v3meta:
-        _v3meta = augmented_station_metadata(v3inv, format='v3')
+        _v3meta = augmented_station_metadata(v3inv, format='giss_v3')
     return _v3meta
 
 def magic_meta(path):
@@ -1402,7 +1446,7 @@ def open(self_, source):
                 ghcn3file = os.path.join('input', source+'.qca.dat')
             invfile = 'input/v3.inv'
             return GHCNV3Reader(file=open(ghcn3file),
-              meta=augmented_station_metadata(invfile, format='v3'),
+              meta=augmented_station_metadata(invfile, format='giss_v3'),
               year_min=code.giss_data.BASE_YEAR)
         if source == 'ghcn.v2':
             return GHCNV2Reader("input/v2.mean",
@@ -1424,7 +1468,11 @@ def open(self_, source):
         if source.endswith('.v2'):
             # A "generic" source.  "ca.v2" will look for ca.v2.mean,
             # ca.v2.inv, ca.tbl (all in the input directory).
-            return read_generic(source)
+            return read_generic_v2(source)
+        if source.endswith('.dat'):
+            # A "generic" v3 source. metadata for "isti.dat"
+            # will come from "isti.inv".
+            return read_generic_v3(source)
         raise Exception("Cannot open source %r" % source)
             
 # Each of the stepN_input functions below produces an iterator that