Blinding and anosmia in male rats is followed by retarded bodily development, reduced weights of the gonads and adnexa, and depressed levels of pituitary luteinizing hormone and prolactin. The effects of dual sensory deprivation are negated, for the most part, by either pinealectomy or the weekly subcutaneous implantation of melatonin (in beeswax). This is the first report that melatonin negates the antigonadotrophìc influence of the rat pineal gland.