We have proposed that colonies of cells with blastlike morphology growing in culture are derived from a blast subpopulation with high proliferative potential. To test whether or not these blast progenitors have the capacity for self-renewal, blast colonies grown from the peripheral blood of the 21 patients with acute myeloblastic leukemia were replated; secondary colonies were observed in 17 instances, and these were similar to primary colonies in size, morphology, and culture requirements. Great patient-to-patient variation was observed in the frequency of secondary colonies, but low secondary plating efficiency was significantly correlated with successful remission induction. We conclude that the blast progenitors detected in the assay have at least limited self-renewal capacity and that this capacity may, along with other risk factors, contribute to clinical outcome.