For safe autografts with peripheral blood hematopoietic cells (PBSCT), better methods for determining the kinetics of stem cell populations and predicting engraftment speed after PBSCT need to be established. Current methods include culture in semi-solid medium and measurement of CD34 cell surface antigen. In this study with only partially purified blood cells obtained from children with cancer in remission, we compared the effects of phytohemagglutinin-stimulated lymphocyte-conditioned medium (PHA-LCM) and recombinant human cytokines on the growth of progenitor cells in a methylcellulose culture system. Interleukin-3 (IL-3) alone supported more progenitor growth than standard PHA-LCM by a factor of 1.54 for colony-forming unit granulocyte/macrophages (CFU-GM) and by a factor of 1.84 for burst-forming unit/erythroids (BFU-E). No significant change, in terms of the number of growing colonies, was observed by adding granulocyte/macrophage colony-stimulating factor (GM-CSF), granulocyte-CSF (G-CSF), or IL-1 to IL-3. However, the addition of G-CSF resulted in increased colony size. A further increase in CFU-GM growth was observed by the addition of IFN-gamma to the combination of cytokines. No significant effect was observed when stem cell factor (SCF) was added to the combination of cytokines containing IL-3, G-CSF, and IFN-gamma. This analysis suggests that the combination of IL-3, G-CSF, and IFN-gamma may provide sufficient stimulation for the growth of human blood cells. The effects of different oxygen tensions on progenitor growth in the presence of IL-3, G-CSF, and IFN-gamma were also evaluated.(ABSTRACT TRUNCATED AT 250 WORDS)