In this study we have evaluated the influence of sex, gonadectomy and sex hormones on the development of L-NAME-induced hypertension in the rat, focusing our investigation on blood pressure (BP), plasma renin activity (PRA), cardiac hypertrophy and proteinuria. Three experiments were performed to investigate: (i) the influence of sex on the development of L-NAME-induced hypertension; (ii) the effects of gonadectomy on the dimorphism of L-NAME-induced hypertension; and (iii) the effects of testosterone in ovariectomized female and of 17beta-oestradiol in orchidectomized male rats. Male L-NAME-treated rats had higher BP values than females. Orchidectomy of L-NAME-treated rats reduced BP to the levels of females and ovariectomy did not affect hypertension in females. Oestrogenized and orchidectomized males had a BP level similar to intact female L-NAME-treated rats. However, androgenization and ovariectomy did not change BP in female L-NAME-treated rats. PRA was greater in intact male L-NAME hypertensive rats than in female rats, and gonadectomy protected against the increase in PRA such that PRA was similar among all the groups. Intact female hypertensive rats showed significantly greater ventricular hypertrophy compared with male hypertensive rats. Male L-NAME hypertensive rats had increased proteinuria that was not present in female rats. Moreover, testosterone increased proteinuria in males and females regardless of the BP level. Male L-NAME-treated rats developed higher BP, PRA and proteinuria than female rats, but were more resistant to the development of cardiac hypertrophy. The higher PRA of male L-NAME-treated rats might be involved in the sex-dependent dimorphism of this model of hypertension.