The possible role of nitric oxide (NO) and vasoactive intestinal polypeptide on isoprenaline-induced relaxation of the mouse longitudinal gastric fundal strips precontracted with 5.4 X 10(-7)M carbachol was investigated. Isoprenaline (5 X 10(-7)M, 10(-6)M and 5 X 10(-6)M) produced a concentration-dependent relaxations. N-G-nitro L-arginine (10(-4)M) partly inhibited isoprenaline-induced relaxation. The inhibitory action of N-G-nitro L-arginine was reversed by 4 X 10(-4)M L-arginine but not by 4 X 10(-4)M D-arginine. N-G-nitro L-arginine (10(-4)M) did not affect the relaxation caused by sodium nitroprusside (10(-6)M). Vasoactive intestinal polypeptide antibody 7913 (1:160 dilution) partly inhibited isoprenaline-induced relaxation, This inhibition was greater on the response to the higher isoprenaline concentration (5 X 10(-6)M) than to the lower concentration (10(-6)M). The combination of vasoactive intestinal polypeptide antibody and N-G-nitro L-arginine significantly enhanced the inhibition on 10(-6)M isoprenaline action. These results suggest that nitric oxide and vasoactive intestinal polypeptide may partly contribute to the relaxation induced by isoprenaline in the mouse gastric fundus precontracted with carbachol.