Histocompatibility antigen (HLA) phenotypes of 34 patients with Ph1+ chronic myelogenous leukemia (CML) were evaluated for association with HLA antigens. Two control populations were compared to the CML patients: 142 normal volunteer platelet donors, and 160 normal donors of granulocyte transfusions. HLA typing was done by lymphocyte microcytotoxicity tests for nine antigens on sublocus A and 15 antigens on sublocus B. HLA-B7 and HLA-B12 were decreased in CML patients compared to both platelet and granulocyte donors. There was increased frequency of HLA-A3 in patients (41%) as compared to controls (25% and 33%); HLA-B5 - patients = 20%; controls 8% and 6%; and HLA-BW17 - patients = 17%; controls = 6% and 3% (P = 0.01). Median survival was 24+ months and independent of HLA. HLA-B5 and HLA-BW17 were significantly increased in patients with CML compared to two normal control populations. No increase in HLA-B8 was seen. Decreased frequency of HLA-B7 and B12 was noted. The significance of these differences is being evaluated.