The BN rat myelocytic leukemia was transferred to (LEW .times. BN)F1 rats. In the F1 host the growth, dissemination and response of this leukemia to chemotherapy were predictable, stable through serial passage and similar to this leukemia''s behavior in the parent strain. Rats given 107 spleen cells i.v. from leukemic donors died in about 3 wk if untreated or responded to cytosine arabinoside even after overt leukemia developed. This animal leukemia is useful as a model for human acute myelocytic leukemia.