Pinealectomy was performed on rat foetuses aged 16.5 days +/- 8 h. Sham-pinealectomized animals were bred under the same conditions. Animals were killed when 50 or 64-days old. Plasma LH response to Gn-RH (100 ng via carotid artery) was studied in undisturbed adult male rats. 1. Body weight at birth was higher in pinealectomized rats than in sham-pinealectomized animals but, in 50 or 64-day-old body weights were not different. 2. In 50-day-old pinealectomized rats, absolute weights of testis and epididymis were higher than in sham-pinealectomized animals. When organ weights were compared to body weight by analysis of covariance, only the epididymis weight was enhanced by pinealectomy. 3. In 64-day-old animals, foetal pinealectomy did not increase reproductive organ weights. In contrast, prostate weight was decreased after pineal removal. 4. Plasma and pituitary gonadotropins were not modified by foetal pinealectomy. In undisturbed adult male rats, the plasma LH response to Gn-RH administration was identical in pinealectomized rats and in sham-pinealectomized animals. These findings may suggest an inhibitory effect of the pineal and foetal growth, but foetal pinealectomy exerts no gonadal stimulation in the adult male rats.