Eight bovine ovaries with a corpus luteum were perfused for 4 h in a haemoglobin-free semi-synthetic perfusion medium in a closed circuit. After an initial prolactin (PRL)-free perfusion phase, 4.7 ng/ml ovine PRL was added in the 1st h, followed by 47 ng/ml in the 2nd h and 470 ng/ml in the 3rd h. Glucose and oxygen consumption and the production of lactate, pyruvate and CO2 were measured, while perfusion pressure and pH-value were recorded continuously. Under the influence of PRL anaerobic glucose metabolism was stimulated by 40.5% and oxidative phosphorylation was inhibited. Energy production from aerobic glucose metabolism rose by only 0.25%. Unlike PRL, Human Menopausal Gonadotropin (hMG) and Human Chorionic Gonadotropin (hCG) stimulated aerobic metabolism. This may indicate that PRL is the "older" hormone in phylleogenetic terms.