In 1986, a total of 2781 laboratories subscribed to the Comprehensive Blood Bank Survey of the College of American Pathologists (CAP) (Skokie, Ill). Performance of these laboratories on the ABO and Rh challenges was good, with 99.7% to 99.9% of the participants reporting the correct response. Antibody identification showed less consistency (45.4% to 97.5%). These challenges consisted of two serum samples with multiple antibodies, one serum sample with antibody to a high-incidence antigen, and one serum sample with anti-M. Performance on the cross match ranged from 95.0% to 99.8% correct, with one exception. This exception was an intended incompatible cross match with the serum containing anti-M, which was reported as incompatible by 56.2% of participants. The antigen-typing challenges ranged from 98.3% to 100% correct, but three typings proved to be a problem. Two samples, when typed for the c antigen, were correctly typed 70.4% of the time and 50.1% of the time. One of these samples, when typed for the E antigen, was correctly typed only 30% of the time. This discrepancy proved to be the result of inadvertent pooling of units of different phenotypes in the sample preparation process.