The effect of the acute or chronic administration of sulpiride on serum prolactin and gonadotropin levels was studied in castrated male rats. Sulpiride administered in acute intravenous injections induced a quick increase in serum prolactin levels and no significant changes in serum gonadotropins. The peak in serum prolactin was observed 30 min after the injection of sulpiride, with a decrease of serum prolactin levels at 60 and 120 min. The subcutaneous administration of sulpiride for 13 days induced a significant increase in serum prolactin levels at the end of the treatment, and no significant changes in serum FSH and LH levels.