Rats were subjected to unilateral renal artery clamping for 60 min and contralateral nephrectomy. <sup>125</sup>I-labelled fibrinogen and <sup>131</sup>I-labelled albumin were injected intravenously 24 h before the experiment. A significant increase in the fibrinogen and albumin content and weight was found already 5 and 15 min after reflow. Rats given heparin (2,000 IU/kg body weight) 5 min before clamping and killed 15 min after reflow showed significantly smaller increases in these values than rats given saline. Morphological studies showed fibrin deposition in Bowman’s space, tubules and peritubular capillaries. The results indicate that fibrin deposition occurs and is of importance in the development of renal edema in this type of renal damage.