l h e purpose of this study was to determine the effect of' immunosuppressive drugs on the production of inflammatory cytokines and on the generation of macrophages from bone marrow precursors. Lipopolysaccharides t i m ii I ate d peripheral blood mononuc lear cells IPBMCs) were cultured in the presence of therapeutic concentrations of 6-mercaptopurine (6-MP). methotrexatc ( M T X ) , or prednisolone. The effect of these drugs on the expre\sion of interleukin (IL)-lp, IL-8, and tumor necrosis factor-a (TNF-a) was studied using bioassays and Northern analysis. The generation of monocytes/ macrophages from precursors in the bone marrow was examined by culturing murine bone marrow cells with macrophage colony-stimulating factor (M-CSF) in the Ulcerative colitis and Crohn's disease are inflammatory bowel diseases (1BDs) characterized by chronic inflammation, with remissions and relapses of active inflammation and clinical disease. Despite the fact that every limb of the immune system is activated, no microbial or dietary factor has been found to explain the pathogenesis of the disease (I). A number of agents have been empirically used in the treatment of patients with IBD. The treatment of refractory cases has used immunosuppressive drugs such as 6-mercaptopurine (6-MP) and, more recently, low-dose pulse methotrexate (MTX; 2-5). Both of these drugs have been found to be efficacious in refractory disease, but their mechanism(s) of action remains unclear. Patients can relapse