The urinary fibrin/fibrinogen degradation products (FDP), as sensitive indicators of various renal disorders, have been measured by several methods. For their determination, a new and highly sensitive enzyme-linked immunosorbent assay not requiring the urine concentration has been developed. The study comprised 42 patients with nonnephrotic chronic glomerulonephritis (CGN), 23 patients with primary nephrotic syndrome (NS), and 29 healthy adults. The results were as follow: (1) the content of urinary FDP in normal subjects was 10.30 ± 9.08 ng/ ml; (2) the mean level of urinary FDP in both CGN and NS groups was significantly higher than in normal subjects; (3) in the CGN group itself there was a tendency for an increase of urinary FDP during more active forms of the disease, and (4) there was a significant correlation between urinary FDP and urinary protein in the CGN group, whereas no correlation was observed in the NS group. These results suggest that the major part of urinary FDP in the CGN group derives from the increased filtration, while its origin in the NS group is not related to increased filtration only, but may also have involved intraglomerular coagulation abnormalities. The newly developed enzyme-linked immunosorbent assay can detect urinary FDP levels lower than 3.9 ng/ml. Therefore, this method can be of great value in determining the degree of abnormalities of intraglomerular coagulation and fibrinolysis in renal diseases