: The effect of an aproteic diet (Ap) on the reproductive axis in young male rats was studied. Also the refeeding effect at different times after the aproteic diet was studied. The Ap diet was given during 21 days. In refeeding groups, the control diet was given during 2, 4 and 6 weeks after the aproteic diet. We studied the plasmatic testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels. Also the hypothalamic GnRH concentration and in vitro hypothalamic GnRH secretion in basal and induced condition was studied. The total protein deficit produced significant reduction in body, testis, seminal vesicles and prostate weights. This was accompanied with decreased levels of plasmatic testosterone (P<0.02). In this aproteic group there was a significant reduction in LH (P<0.05) and FSH (P<0.05) plasmatic levels. Refeeding with control diet reversed this situation, producing significant increment in LH (P<0.05) and FSH levels (P<0.01) at the fourth and second weeks, respectively. The basal hypothalamic GnRH secretion did not differ from the control; nevertheless the induced secretion was significantly (P<0.05) greater in the aproteic group. Also the hypothalamic GnRH concentration was increased (P<0.05) in animals fed with the aproteic diet. The minor testis, prostate, and seminal vesicles" weight, and a decreased plasmatic testosterone in rats fed with an aproteic diet, are produced by a decrease in gonadotrophin secretion. This decrease in turn is caused by a reduction in GnRH secretion, since hypothalamic GnRH concentration is increased in rats fed with the aproteic group, and induced secretion is greater in this group. All these alterations produced by an aproteic diet are reversible, since-with contol diet refeeding-the gonadotrophin secretion returned at control levels.