A case is reported of an adult male patient with acute leukemia characterized by the presence of the novel cytogenetic abnormality, t(2;9)(p12;p23), in addition to a t(4;11)(q21;q23). The immunophenotype of the blast cell population was consistent with immature early pre-B cell acute lymphoblastic leukemia (ALL) (TdT+,HLA-DR+,CD19+,CD24±,CD10-) expressing myelo-monocytic antigens (CDw65,CD15). The genotype showed a clonal rearrangement of the immunoglobulin heavy chain locus. Because the immunoglobulin kappa (κ) light chain gene is located on chromosome 2 at band p12 and interferon alpha (α) and beta (β) map to chromosome 9p21-p22, rearrangements of these loci as a result of the t(2;9) were studied. There was no evidence for rearrangement of the region covering about 40 kilobases around the κ locus when hybridized to C(κ), the 3′ κ enhancer or the κ deleting element. Only germline size restriction fragments were also found for the interferon α and β genes. The patient's clinical features were typical for ALL associated with the t(4;11), including a high white blood cell count at presentation, hepatosplenomegaly, and a poor outcome. The potential significance of 2p and 9p abnormalities in addition to t(4;11) is discussed.