We have analysed the configuration of immunoassociated genes and the karyotypes of 30 patients with acute myelocytic leukemia (AML) and 10 with chronic myelocytic leukemia in blast crisis (CML-BC). In AML, the frequencies of T-cell receptor (TcR) beta, gamma, and delta chain and immunoglobulin heavy and light chain gene rearrangements were 4.2%, 19%, 8%, 10.7% and 10.5%, respectively. In CML-BC, they were 10%, 20%, 40%, 50% and 0%, respectively. Nine patients had abnormalities in chromosome 2, 7 or 14, upon which immunoassociated genes are located. There seems to be no apparent relationship between these chromosome abnormalities and gene rearrangements. In all patients but one (5/6), the delta rearrangement was accompanied by other immunoassociated gene rearrangements. Molecular size analysis revealed specific delta rearranged band(s) (19.5 kb-BamHI and/or 6.9 kb-EcoRI), as commonly detected in B-acute lymphocytic leukemia (ALL). All the patients with the delta rearranged band, however, had a germline configuration of J delta gene loci, suggesting a DD or V(D)D (probably V delta 2(D)D) pattern. This study also indicates that the delta rearrangement is specific in AML or CML-BC and distinct from that in early T leukemia/lymphoma.