The Hu-ets-1 oncogene was found to be rearranged and amplified 30-fold in one case of acute myelomonocytic leukemia in which a homogeneously staining region occurred on 11q23; the oncogene was rearranged and amplified approximately tenfold in a case of small lymphocytic cell lymphoma with an inverted insertion that also involved band 11q23. This work suggests that Hu-ets-1 is an unusual oncogene that can help explain the common involvement of chromosome band 11q23 in various subtypes of hematopoietic malignancies.