The possibility that tumor necrosis factor (TNF) and interleukin-1 (IL-1) could participate in the development of diabetic nephropathy was evaluated in streptozocin (STZ)-treated diabetic rats. Diabetic rats were divided into two groups: aminoguanidine treated group (25 mg/kg body wt, daily i.p. injection; DM-AG group) and untreated group (DM group). Non-diabetic age-matched rats were also divided into two groups with the same manner and used as controls. After twelve weeks of treatment, glomerular basement membranes (GBM) were isolated from rats of each experimental group. When thioglycollate-elicited peritoneal macrophages (M phi) from normal rats were incubated with these GBM materials, GBM from DM group induced significantly greater levels of TNF and IL-1 production than did GBM from other three groups with at doses of 2.5 to 10 mg. The TNF and IL-1 production by stimulation of GBM from the DM-AG group were similar to those from each control group. Aminoguanidine treatment significantly decreased the accumulation of advanced glycation end-products (AGEs) in GBM of diabetic rats. These findings suggest that AGE-proteins may be involved in the production of TNF and IL-1 from M phi. AGE-induced cytokines may be implicated in the development of diabetic nephropathy.