Acute nonlymphocytic leukemia (ANLL) was diagnosed in 18 patients based on morphological, cytochemical and immunological criteria. Leukemic cells of these cases were subjected to Southern blot analysis and subsequent hybridization to heavy chain immunoglobulin and T-cell-receptor gene probes. A rearrangement within the immunoglobulin joining region was detected in 2 cases, while the T-cell-receptor beta-chain gene was in germline configuration in all samples investigated. These data confirm recent reports indicating that immunoglobulin heavy chain gene rearrangements are not restricted to B-lineage neoplasms.