Intravascular coagulation localized in glomeruli is of pathologic importance in human and experimental GN. The measure of fibrinogen related antigen (FRA) in serum and urine after concentration (Merskey's technique) was used to detect and estimate this phenomenon. In Rabbit Masugi GN, FRA were detected in urine 5 to 20 mg/24 h, in close correlation with the amount of proteinuria, the intesity of histological changes and the presence of fibrin deposits in glomeruli. In human GN, urine FRA were detected in many cases (0,5-10 mg/24 h) in correlation with the histological type of lesions (FRA + in primary or secondary proliferative GN) and with the evolutivity of disease (FRA + in cases with rapidly progressive kidney function deficiency). Urine FRA are also in correlation with intraglomerular fibrin deposits : this suggests that urine FRA originate from lysis of fibrin deposited within glomeruli. So urine FRA appears to be an indicator of type and severity of GN and probably of therapeutic measures, indicating anticoagulant and/or antithrombic therapy : the variations of urine FRA during treatment is of value to assess the effects of these drugs and to establish the prognosis of the disease.