The colony-stimulating factor-containing supernatant of the human trophoblast cell line TPA-30-1 was used to stimulate in vitro growth of acute myeloid leukemia clonogenic cells from 54 patients. Prevalent colony growth (10-greater than 1000) was observed in 63% of cases. In 31% clusters and a few colonies (1-9/1 x 10(5) plated cells) were scored. Neither colonies nor clusters could be detected in the remaining 6%. The best growth was observed in subtype M5 (8 of 9 cases, 89%). Morphological examination and recloning tests suggested that the colonies originated from leukemic progenitors. TPA-30-1 supernatant stimulation can therefore be compared with that of phytohemagglutinin or phytohemagglutinin-leukocyte-conditioned medium. In addition it does not require T-lymphocyte removal and batch screening. Extension of the culture for antigenic characterization of acute myeloid leukemia clonogenic cells to more patients than in a previous study confirmed the existence of a subgroup (39%) of patients whose acute myeloid leukemia clonogenic cells constantly expressed late myeloid differentiation antigens recognized by the monoclonal antibody S4-7. Since S4-7 spares early normal hemopoietic progenitors, this subgroup (54% M2) can be considered as candidates for autologous bone marrow transplantation after in vitro purging with S4-7 monoclonal antibody and complement.