The passages 0 and 3 purified human bone marrow fibroblast layers (FLs) were established by long-term liquid cultures. After 12-day coculture of stromal. cell-depleted marrow cell suspensions with passage 0 FLs, 68.33 +/- 4.04% of the hemopoietic colonies adhered to FLs was myeloid in nature and the other 31.67 +/- 4.04% was erythroid. There were still CFU-E (colony forming unit-erythroid), BFU-E (burst forming unit- erythroid), and CFU-GM (colony forming unit-granulocyte/macrophage) among the nonadherent cells. The media conditioned by passage 0 (F0-CM) and passage 3(F3-CM) FLs stimulated the growth of myeloid and erythroid (BFU-E) colonies. From these data, it is concluded that both FLs and the media conditioned by fibroblasts can stimulate myeloid and erythroid hemopoiesis.