Abstract
A particle of discrete biochemical composition was purified from fresh, unfrozen peripheral blood leukocytes of human patients with acute myeloblastic leukemia. This particle endogenously synthesized DNA by use of an RNA primer and template. About half of the DNA sequences synthesized in the presence of actinomycin D hybridized to RNA isolated from type-C sarcoma viruses of primates or mice; lower annealing values were obtained with RNA isolated from other sarcoma or leukemia viruses. The results confirm and extend previous results from molecular hybridization experiments related to the existence in human leukemia of components of RNA tumor viruses.