The activities of tuberoinfundibular and tuberohypophysial dopamine (DA) neurons were estimated by measuring the turnover of DA in terminals of these neurons in the median eminence and in the neural and intermediate lobes of the pituitary, respectively. The rate of DA turnover (alpha-methyltyrosine-induced decline of DA) in the median eminence was two to three times faster in females than in males, but no sexual differences in DA turnover rates were noted in the neural and intermediate lobes. Two weeks following gonadectomy the rate of DA turnover in the median eminence was increased in the male but decreased in the female. These effects were reversed by testosterone and estrogen replacement in gonadectomized males and females, respectively. Neither gonadectomy nor steroid replacement altered DA turnover in the neural or intermediate lobes of either males or females. These results indicate that estrogen stimulates and testosterone inhibits tuberoinfundibular DA neuronal activity while neither steroid affects tuberohypophysial DA neuronal activity.