The origin of free cells in urine is difficult to determine in the absence of cellular casts. Using fluorescein-conjugated antibody to human Tamm-Horsfall protein (THP), it examines THP coating of free cells in urine (THP-CFC), that could be distinguished between renal parenchymal disease (RPD) and lower urinary tract disease (LUTD). We had examined THP-CFC in urine of the patients with all kinds of RPD, renal or ureteral stone (RUS) and LUTD. The percentage of THP-CFCs was 0% in healthy volunteers (n = 34), 0-8% in LUTD group (n = 14), 86.3% in glomerulonephritis and SLE nephritis group (n = 29), 80.8% in chronic intertitial nephritis group (n = 26), 0-10% in RUS group (n = 14). The research results suggest that the percentage of THP-CFCs between the RPD and LUTD or RUS had a significant difference. The presence of THP-CFC in RPD and its absence in LUTD suggests that this simple test may be of use in differentiating RPD from LUTD.