The effect of DL-propranolol on the production of nitric oxide (NO.) by cultured arterial smooth muscle cells from normotensive (WKY) and spontaneously hypertensive rats (SHR) was studied before and after stimulation by lipopolysaccharide or interleukin-1 beta. The influence of L-arginine and NG-nitro-L-arginine on these events was also studied. Lipopolysaccharide-stimulated SHR-derived smooth muscle cells produced less NO. than WKY cells. However the amounts produced in response to interleukin-1 beta were similar for the two cell types. DL-propranolol increased the NO. production in both types of cells exposed to lipopolysaccharide, but had no significant effect on this parameter in WKY-derived cells exposed to interleukin-1 beta. Inclusion of L-arginine during incubations with propranolol had no effect on the levels of NO. produced by either cell type exposed to lipopolysaccharide. The basal production of NO. was enhanced in smooth muscle cells from both normotensive and hypertensive rats when the cells were treated with L-arginine after exposure to interleukin-1 beta. L-Arginine increased the response to DL-propranolol only in the WKY cells. NO. production was depressed by inclusion of NG-nitro-L-arginine during incubations in both cell types regardless of the treatment regime used to induce NO. synthase activity. The results suggest that DL-propranolol may induce the production of NO. by cultured smooth muscle cells exposed to cytokines.