Turnover of the tubero-infundibular dopamine (DA) neurons was studied with the help of the tyrosine-hydroxylase inhibitor α-methyl-tyrosine-methylester (H 44/68) in immature female rats injected with pregnant mare serum gonadotrophin (PMS) in the morning of day 30. The rats were killed 2–4 h after the injection of H 44/68, and amine turnover was estimated by studying the decline of DA stores in the median eminence, using the histochemical fluorescence analysis of DA. It was found that DA turnover remained low during the ‘critical period’ (3–5 p. m. on day 32) in the PMS-treated rats when compared with saline-injected controls. On the following morning (day 33), DA turnover was very high compared with the control rats, and in the morning of day 32 the turnover was slightly increased. Daily injections of testosterone propionate to the PMS-treated rats blocked ovulation and markedly increased amine turnover in the tubero-infundibular neurons during the ‘critical period’ compared with rats treated with PMS alone. The present results support the theory that the tubero-infundibular DA neurons might act to inhibit LRF release from the median eminence and are compatible with the view that the tubero-infundibular DA neurons could partly mediate the inhibitory feed-back action of testosterone on LRF release from the median eminence.