The potential role of oxygen free radicals in hCG-induced ovulation was investigated using the free radical scavenging enzymes superoxide dismutase (SOD) and/or catalase with the in-vitro perfused rabbit ovary preparation. SOD (25 μg/ml) and SOD + catalase (25 μg/ml) significantly reduced the % of large follicles that ovulated during perfusion (P < 0.005). Neither maturity nor degeneration of ovulated ova and follicular oocytes was affected by SOD and/or catalase. Progesterone concentration in the perfusate was significantly increased in the SOD + catalase treatment group (P < 0.01). These results indicate a significant role for oxygen free radicals in the process of ovulation.