We have examined the effects of oxygen free radicals, generated by xenobiotics administration, ischaemia-reperfusion or sepsis, on the healing of skin or intestinal wounds in rats. We found that 5 days after operation there was a significant decrease in the wound breaking strength in rats treated with phenazine methosulfate, zymosan, ischaemia-reperfusion or retroperitoneal infection. These changes were specifically prevented by administration of superoxide-dismutase (SOD), aprotinin and (in some models) allopurinol. On the contrary, none of these measures was effective when a local trauma caused the decrease in breaking strength. Our results suggest that oxygen free radicals mediate the inhibition of wound healing following ischaemia-reperfusion and sepsis.