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, but incompletely, reduced fibrinolytic activity measured 24 hours after operation. Fibrinopurulent peritonitis induced by creation of a 10 centimeter long ischemic loop of the terminal part of the ileum abolished the fibrinolytic activity of the peritoneum almost completely. The data are consistent with findings that adhesion formation is inversely correlated with the fibrinolytic activity of the peritoneum. Untreated peritonitis abolished that activity by mechanisms as yet not elucidated. Heparin, which has been shown to reduce both adhesion-formation and the lethality of peritonitis, apparently does so by mechanisms independent of the intrinsic fibrinolytic system of the peritoneum.