SummaryThis study explores the effects of several divalent metal ions on thein vitroproduction of cyclic AMP, cyclic GMP, and testosterone by rat testicular tissue and on the amount of binding of [125I]human chorionic gonadotropin (hCG) in the testis. Zn2+at concentrations of 10-6to10-4M enhanced the hCG-stimulated production of cyclic AMP and testosterone, but only in the presence of Ca2+. [125I]hCG binding to rat testicular tissue was not affected by Zn2+. Cu2+, Ni2+, Co2+, and Mn2+ did not increase cyclic AMP or testosterone production in concentrations of 10-7to 10-3M and even inhibited them at a high concentration (10-2M). Cyclic GMP production was not affected by these divalent ions. These results suggest that Zn2+may play an important role in rat testicular steroidogenesis.