The levels of pituitary and gonadal hormones were measured by radioimmunoassay during a long-term (12-month) therapy with prazosin and its combination in 23 patients aged 30-59 years who suffered from Stage II hypertensive disease. Prazosin monotherapy resulted in a significant decrease in prolactin levels, followed by inhibited elaboration of luteinizing, follicle-stimulating, and testicular hormones in the first 6 months of therapy without changing estradiol levels. The hypoprolactinemic effect of prazosin was significantly enhanced with an increase in therapy duration and more profound in patients who had high baseline prolactin levels and in younger patients. Prazosin in combination with nadolol was found to level off the hyperprolactinemic effect of the latter without potentiating the reduction in the levels of follicle-stimulating, luteinizing, and testicular hormones which was observed during therapy with each drug alone.