Derangement of the hemopoietic progenitor cells has been observed in the majority of patients with the acquired immunodeficiency syndrome (AIDS). In this study the effect of recombinant human GM-CSF was evaluated for the in vitro growth of hemopoietic progenitor cells from the bone marrow of patients with AIDS. A significant reduction of growth (mean +/- SEM) of CFU-GEMM (2.5 +/- 1.2), BFU-E (23 +/- 9), and CFU-GM (55 +/- 21) was found in AIDS patients in comparison to normal controls. There was a linear correlation between the number of CFU-GM growing in vitro after stimulation with rh GM-CSF as compared to medium conditioned by phytohemagglutinin-stimulated leukocytes (PHA-LCM). However, CFU-GM from patients with AIDS appear to need higher concentrations of rh GM-CSF for maximal growth.