A preliminary study of the culture of leukemic progenitor cells (CFU-L) from acute non-T lymphoblastic leukemia was undertaken for 25 patients (19 were considered in complete remission and 6 in the acute phase of the disease). Two culture systems were tested; a double layer agar-liquid phase and a single layer of methylcellulose. The major problem was the characterization of the colonies: immunological labelling coupled with cytofluorometry, as well as cytomorphology, cytogenetic and more recently molecular biology may allow the characterization of the CFU-L. The culture of CFU-L appears to be an efficient method for detecting residual leukemic cells which can be used to evaluate the quality of both the remission obtained and that of autologous bone marrow after purging.