The effect of laparotomy, intestinal resection, heparin and bacterial peritonitis on fibrinolysis of the peritoneum was evaluated in dogs. Heparin had no effect. Sterile laparotomy and intestinal resection severely reduced fibrinolytic activity measured 24 h after operation. Fibrinopurulent peritonitis induced by creation of a 10 cm long ischemic loop of the terminal part of the ileum abolished the fibrinolytic activity of the peritoneum almost completely. Adhesion formation is inversely correlated with the fibrinolytic activity of the peritoneum. Untreated peritonitis abolished that activity by unknown mechanisms. Heparin, was shown to reduce adhesion formation and the lethality of peritonitis and apparently does so by mechanisms independent of the intrinsic fibrinolytic system of the peritoneum.