diff --git a/doc/src/sgml/ref/set.sgml b/doc/src/sgml/ref/set.sgml
index ec4b1baa89..2b203e7698 100644
--- a/doc/src/sgml/ref/set.sgml
+++ b/doc/src/sgml/ref/set.sgml
@@ -545,6 +545,11 @@ SET TIME ZONE { '<REPLACEABLE CLASS="PARAMETER">timezone</REPLACEABLE>' | LOCAL
 	   <para>
 		Sets the isolation level for the current transaction to
 		'SERIALIZABLE' or 'READ COMMITTED'.
+		SERIALIZABLE means that the current transaction will place a 
+		lock on every row read, so later reads in that transaction 
+		see the rows unmodified by other transactions.
+		READ COMMITTED means that the current transaction reads only 
+		committed rows.  READ COMMITTED is the default.
 	   </para>
 	  </listitem>
 	 </varlistentry>
@@ -557,7 +562,7 @@ SET TIME ZONE { '<REPLACEABLE CLASS="PARAMETER">timezone</REPLACEABLE>' | LOCAL
 	  <listitem>
 	   <para>
 		Sets the isolation level for the current transaction to
-		'SERIALIZABLE' or 'READ COMMITTED'.
+		'READ COMMITTED'.
 	   </para>
 	  </listitem>
 	 </varlistentry>
diff --git a/src/man/set.l b/src/man/set.l
index 9a4cf7f9fb..15c64baca7 100644
--- a/src/man/set.l
+++ b/src/man/set.l
@@ -1,6 +1,6 @@
 .\" This is -*-nroff-*-
 .\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/set.l,v 1.20 1999/06/03 20:44:28 momjian Exp $
+.\" $Header: /cvsroot/pgsql/src/man/Attic/set.l,v 1.21 1999/06/04 03:44:42 momjian Exp $
 .TH SET SQL 05/14/97 PostgreSQL PostgreSQL
 .SH NAME
 set - set run-time parameters for session
@@ -86,6 +86,14 @@ sets the current transaction's isolation level to
 .IR SERIALIZABLE
 or
 .IR READ COMMITTED .
+.IR SERIALIZABLE
+means that the current transaction will place a lock on every row read,
+so later reads in that transaction see the rows unmodified by
+other transactions.
+.IR READ COMMITTED
+means that the current transaction reads only committed rows.
+.IR READ COMMITTED
+is the default.
 .PP
 .IR CLIENT_ENCODING|NAMES
 sets the character set encoding of the client.  Only available if multi-byte