Spontaneous complete remission of four months' duration was observed in a 51-year-old male with hypoplastic leukemia. Cytogenetical analysis revealed that leukemia cells of this patient were tetraploid. The diameter of leukemia cells involving myeloid cells ranged from 30 to 50 mu. The remission was apparently associated with repeated blood transfusions and severe infection. Complete remission was confirmed by normal morphology and karyotype of the bone marrow cells, although in vitro marrow stem cell growth did not return to normal. Thus, normal hematopoiesis may not have recovered when the diagnosis of spontaneous remission was made.