1. The turnover of fibrinogen was studied in twenty-eight patients after moderate and major surgical operations and in a contrast group of thirteen patients suffering from miscellaneous chronic disorders.
2. After operation the mean biological half-life of fibrinogen was 60.1 h (SD 16.4) and the mean plasma loss of fibrinogen was 40.1% (SD 12.6) of the intravascular fibrinogen pool each 24 h. In the contrast group, respective values of 96.2 h (SD 13.1) and 22.5% (SD 2.0) were obtained, which are in agreement with published values for the normal catabolism of fibrinogen.
3. When the post-operative increase in the plasma fibrinogen pool was taken into account, a massive increase in the absolute plasma loss of fibrinogen was observed with values approaching those reported for albumin turnover.
4. Possible sites of loss and the relevance of this investigation to the detection of disseminated intravascular coagulation and venous thrombosis are discussed.