The present studies were designed to assess the ability of primary cultures of bone marrow cells to produce nitric oxide. We found that two inflammatory stimuli, IFN-gamma and LPS, were potent inducers of nitric oxide production by bone marrow cells. In addition, the CSF granulocyte-macrophage (GM)-CSF and IL-3 as well as TNF-alpha, while inactive by themselves, were synergistic with LPS and IFN-gamma in inducing nitric oxide production. Maximal effects were observed with combinations of GM-CSF and LPS. Nitric oxide production by bone marrow cells was found to be dependent on the presence of L-arginine in the culture medium and inhibitable by NG-monomethyl-L-arginine and L-canavanine, two nitric oxide synthase inhibitors. Nitric oxide produced by the cells was also suppressed by TGF-beta 1 and the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. Separation of bone marrow cells by density gradient centrifugation and flow cytometry revealed that the granulocyte-containing fraction was largely responsible for nitric oxide production. In additional experiments we found that treatment of bone marrow cells with GM-CSF significantly stimulated bone marrow cell growth. In contrast, the combination of GM-CSF and LPS or IFN-gamma markedly suppressed cellular proliferation. This suppression was completely reversed by treatment of the cells with NG-monomethyl-L-arginine. Taken together, these data demonstrate that various inflammatory stimuli and cytokines induce nitric oxide production by primary cultures of bone marrow cells and that this mediator may play a role in the regulation of bone marrow cell growth and development.