A number of specific chromosomal abnormalities have been associated with distinctive clinical and/or morphological subtypes of acute nonlymphocytic leukemia (ANLL) in recent years. We have studied three patients with ANLL and t(1;3)(p36;q21). Each had weakness as their major complaint, a moderately severe anemia and, for ANLL, a relatively high platelet count. All three demonstrated abnormalities of the megakaryocytic, erythroid and granulocytic lineages. Most striking was the dysmegakaryocytopoiesis. The blasts in all three patients showed relatively few azurophilic granules, one to four prominent nucleoli, and rare peroxidase positivity. No patient had Auer rods. No patient responded to standard chemotherapy regimens. The data suggest that t(1;3)(p36;q21) identifies a new cytogenetic-clinicopathologic subtype of ANLL.