Muscle specimens were obtained from human oviducts during legal surgical sterilizations. Muscle strips (1 mm wide) were dissected from the circular and longitudinal muscle layers at the ampullary-isthmic junction, and contractile activity was recorded during short-term experiments in an organ bath. Administration of copper chloride induced a clear-cut excitatory response in both muscle layers. The response was, in many respects, similar to that evoked by low concentrations of prostaglandin F2α (PGF2α) but differed from the response induced by PGE2. Pretreatment of the tissue with indomethacin blocked the excitatory action of copper and frequently reversed the response into an inhibition of the contractile activity. After maximal stimulation of contractility by exogenous PGF2α, copper was ineffective as a stimulant, whereas a maximal response elicited by copper could be further augmented by the addition of PGF2α. The conclusion is that copper ions released from a copper intrauterine contraceptive device may increase contractility of the oviducts by an action on endogeneous synthesis of prostaglandins, predominantly of the F series. In addition, copper also seems to possess an inhibitory influence on motility of the oviducts, which becomes apparent only when the excitatory effect is blocked pharmacologically.