The aim of this study was to examine if the growth factor, transforming growth factor beta 1 (TGF beta 1), could prevent induction of nitric oxide synthase and cytokine-mediated inhibitory effects in the insulin-containing, clonal beta cell line RINm5F. Treatment of RINm5F cells for 24 h with interleukin-1 beta (IL-1 beta) (100 pM) induced expression of nitric oxide synthase and inhibited glyceraldehyde-stimulated insulin secretion. Combinations of IL-1 beta (100 pM), tumour necrosis factor-alpha (100 pM) and interferon-gamma (100 pM) reduced RINm5F cell viability (determined by the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium (MTT) reduction assay) and de novo protein synthesis, as measured by incorporation of radiolabelled amino acids into perchloric acid-precipitable protein. Pretreatment of RINm5F cells with TGF beta 1 (10 pM) for 18 or 24 h, prior to the addition of either IL-1 beta or combined cytokines, prevented cytokine-induced inhibition of insulin secretion, protein synthesis and the loss of cell viability. TGF beta 1 pretreatment inhibited cytokine-induced expression and activity of nitric oxide synthase in RINm5F cells as determined by Western blotting and by cytosolic conversion of radiolabelled arginine into labelled citrulline and nitric oxide. Chemically generated superoxide also induced expression of nitric oxide synthase possibly due to direct activation of the nuclear transcription factor NF kappa B, an effect prevented by both an antioxidant and TGF beta 1 pretreatment. In conclusion, the mechanism of action of TGF beta 1 in blocking cytokine inhibitory effects was by preventing induction of nitric oxide synthase.