The action of prostaglandins E1 and F2α on adenylate cyclase and cAMP phosphodiesterase was assayed in cell membrane fractions of amnion obtained before and after labor from term physiological pregnancies. Both prostaglandins stimulate the activity of adenylate cyclase in a dose-dependent manner. After spontaneous delivery both prostaglandins stimulate the activity of phosphodiesterase at lower doses and inhibit it at higher ones while the stimulatory effect of low doses is missing before labor. Such a behavior could represent a mechanism for the preservation of the cAMP-mediated processes throughout the entire event of delivery.