We have investigated the role of acute myelogenous leukemia (AML) marrow-derived fibroblastic cells in the development of the hemopoietic microenvironment in vitro, and compared their functional integrity with that of their normal marrow-derived counterparts. Our results indicate that the development of stromal adherent layers in AML long-term marrow culture (LTMC) depends to a large extent on the presence of fibroblastic progenitors (fibroblast colony-forming units, CFU-F) in the bone marrow inoculum. Positive correlations were observed between the numbers of CFU-F in fresh AML marrow samples (nine cases studied) and the numbers of adherent nucleated cells (r = 0.91), adherent CFU-F (r = 0.87), adherent hemopoietic progenitors (r = 0.71), and colony-stimulating factor-1 (CSF-1) levels (r = 0.74) in LTMC. All the above parameters were drastically reduced in LTMC derived from AML marrows that contained low numbers of CFU-F (i.e. below the normal range of 76-130 CFU-F per 10(6) bone marrow cells) when compared with LTMC established from normal marrows. In contrast, no difference was observed in such parameters when normal LTMC and LTMC from AML patients with normal levels of marrow CFU-F were compared. Fibroblast adherent layers derived from AML patients with normal marrow CFU-F numbers produced normal levels of CSF-1 and showed a similar hemopoietic supportive capacity to that of fibroblast layers from normal bone marrow. Thus, our results suggest that (i) the presence of CFU-F in adequate levels in the bone marrow inoculum is critical for the adequate development of the hemopoietic microenvironment in LTMC, and (ii) AML marrow-derived fibroblasts seem to be functionally normal, at least in some AML patients.