Acute myelofibrosis (AMF) was diagnosed in a 59-yr-old black male in September 1978, on the basis of pancytopenia, lack of hepatosplenomegaly, fibrosis of the marrow, and paucity of teardrop red blood cells in the peripheral blood. Since then the patient has demonstrated an unusually long survival of 36 mo with a changing cytogenetic course. His initial 46, XY normal karyotype changed in 20 mo to trisomy 8, followed 1 yr later by 1:4 translocation in peripheral blood. Simultaneously with these changes, the fibrosis in the bone marrow progressively decreased, ultimately terminating in chronic granulocytic leukemia-like presentation with reversal to 46, XY karyotype. Fibroblast culture failed to show any evidence of cytogenetic abnormalities. The disappearance of fibrosis confirmed by trichrome and reticulin stains and lack of cytogenetic abnormalities in fibroblasts confirms the secondary role of fibrosis.