The levels of urinary PIC and FDP were studied in 86 diabetics. Urinary PIC or FDP were detected only in patients representing more than (++) urinary protein, suggesting that urinary PIC is not useful for diagnosis of early stage of diabetic nephropathy. On the other hand, positive rate of urinary PIC was much higher than that of chronic nephritis not due to diabetes mellitus. Plasma levels of PIC were elevated above normal range in all patients with advanced diabetic nephropathy tested. These results suggest that urinary PIC might be derived from circulating blood and reflect the level of systemic fibrinolytic activities in diabetics.