A study was made of the influence of apomorphine. D- and L-amphetamine on the effects of different hormonal treatments used to induce copulatory behavior in female rats. Female copulatory behavior, (lordosis response), which has been shown to be inhibited by increased DA and 5-HT neuronal activity, was depressed by apomorphine, D- and L-amphetamine in ovariectomized rats treated with estrogen + progesterone. When lordosis behavior was activated by estrogen alone the inhibitory action of the drugs, especially that of apomorphine was considerably less pronounced. However, the effect of D-amphetamine on stereotype activity was not greater after treatment with estrogen + progesterone than after administration of estrogen alone. Estrogen had a slight stimulatory effect on stereotype activity in non-drug-treated rats, while progesterone had an inhibitory effect. Possible mechanisms underlying the observed interactive effect of progesterone and monoamines on lordosis behavior, such as a progesterone-induced alteration of monoaminergic transmission, are discussed.