This study reports the effect of a vegetarian diet and dexamethasone administration on the hormone status of healthy Caucasian men and premenopausal women. A lower nocturnal release of prolactin and testosterone occurred in men fed a vegetarian diet, while in women, dexamethasone administration decreased the nocturnal release of prolactin and caused a greater decrease of plasma dehydroepiandrosterone (DHEA). These results show that diet modification can induce hormonal changes, If similar changes occur in patients with breast and/or prostatic cancer, diet modification may be of benefit in these patients with tumors known to be hormonally dependent.