FSH promotes the appearance of LH receptor on granulosa cells during the late stages of their differentiation. The mechanisms by which FSH induces LH receptor are not known, but intracellular cAMP has been implicated. To determine if the induction of LH receptor by FSH might be mediated by cAMP, agents that elevate intracellular cyclic nucleotides were added to cultured granulosa cells. Increasing concentrations of 8-bromo-cAMP (8-Br-cAMP; 0.05–10 mM), 8-bromo-cGMP (8-Br-cGMP; 0.05–10 mM), or cholera toxin (1 × 10-3 to 1 × 106 ng/ml) were added to the cells at the initiation of culture. The LH receptor content and the concentration of progesterone were measured at various times up to 72 h. Each of the agents induced LH receptor, although only cholera toxin was as effective as optimal concentrations of FSH, 8-Br-cAMP (2 mM), 8-Br-cGMP (2 mM), and cholera toxin (100 ng/ml) were maximally effective in inducing receptor. Seventy two hours were required for maximal receptor induction with each of the agents. In contrast to results observed in induction of receptor, 8-Br-cAMP, 8-BrcGMP, and cholera toxin were all as effective as FSH in stimulating progesterone production. The addition of 8-Br-cAMP or cholera toxin with concentrations of FSH optimal for receptor induction gave no increase in receptor content over that occurring with FSH alone. High pressure liquid chromatography revealed that the 8-Br-cGMP was not contaminated with cAMP or 8-Br-cAMP. These results indicate that the induction of LH receptor by FSH is mediated through elevation of cAMP and that the addition of exogenous 8-Br-cGMP can mimic the effects of cAMP.