SUMMARYA mixed antiglobulin test with lymphocytes as test antigens has been developed for the detection of IgG antibodies. Free lymphocytes were counted before and after the addition of anti-D-coated indicator erythrocytes to quantitate the test. The optimal ratio of lymphocytes to indicator erythrocytes was 1: 30. Both anti-T and anti-B lymphocyte antibodies were detected by the test. Nonspecific agglutination of B lymphocytes and detector erythrocytes was avoided by the use of an appropriate dilution of the goat anti-human y chain reagent. Unlike cytotoxicity tests it could be used with dead lymohocytes that were frozen and stored intact as well as with live lymphocytes. Lymphocytes were better test antigens than were kidney cells from the same donors in the test. The mixed antiglobulin test with lymphocytes was also more sensitive in the detection of antibodies in hemodialysis patients than was the microlymphocytotoxicity test.