Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 21156)
+++ wp-includes/query.php	(working copy)
@@ -2187,8 +2187,14 @@
 			$searchand = '';
 			foreach( (array) $q['search_terms'] as $term ) {
 				$term = esc_sql( like_escape( $term ) );
-				$search .= "{$searchand}(($wpdb->posts.post_title LIKE '{$n}{$term}{$n}') OR ($wpdb->posts.post_content LIKE '{$n}{$term}{$n}'))";
-				$searchand = ' AND ';
+				$search_fields = array( "$wpdb->posts.post_title", "$wpdb->posts.post_content" );
+				$search_fields = apply_filters( 'search_fields', $search_fields );
+				if (is_array($search_fields)) {
+					foreach( $search_fields as &$s )
+						$s = "({$s} LIKE '{$n}{$term}{$n}')";
+					$search .= "{$searchand}(".implode( ' OR ', $search_fields  ).")";
+					$searchand = ' AND ';
+				}
 			}
 
 			if ( !empty($search) ) {