The limited value of the antiglobulin phase of the cross match when a careful antibody screening is performed was demonstrated by analyzing 73,407 compatibility tests for 23,857 patients. By the blood grouping and screening of these patients, 178 cases were detected with unexpected blood group antibodies that had not been previously observed. Unexpected antibodies were detected in an additional 13 patients by the saline phase of the cross-match. In addition, the antiglobulin phase disclosed only one patient with a very weak anti-Lea and two patients whose sera gave doubtful reactions, possibly representing antibodies, but too weak to be identified.