Effects of nitric oxide (NO) synthase inhibitors on the enoxacin-induced convulsions were examined in mice pretreated with fenbufen. 7-nitroindazole markedly suppressed the incidence of convulsions, whereas L-arginine did not modify the convulsions at all. The suppression of the convulsions by 7-nitroindazole was not reversed by the pretreatment of L-arginine. Brain NO synthase activity was significantly raised at 30 min after enoxacin when combined with fenbufen. The increased NO synthase activity was found to be suppressed by the pretreatment of 7-nitroindazole. These findings suggest that endogenous NO may be involved as a proconvulsant substance in the development of enoxacin-induced convulsions in mice pretreated with fenbufen.