The differential diagnosis of acute renal failure (ARF) and chronic renal failure (CRF) may be possible by measuring urinary dipeptidase (Udpase) activity and serum creatinine (Scr) concentration. When the mass test of 246 individuals was examined on a 2-dimensional plot of Udpase (y-axis) versus Scr (x-axis) with the data obtained from healthy volunteers (n = 189), ARF (n = 19) and CRF (n = 38) patients, the characteristic distribution of each group was obvious. It is summarized by the mean values of healthy volunteers (1.44 +/- 0.39 mg/dL, 1.19 (0.59 mU/mL), ARF (6.04 +/- 5.04 mg/dL, 0.12 +/- 0.08 mU/mL), and CRF patients (8.72 +/- 2.93 mg/dL, 0.81 +/- 0.44 mU/mL). The healthy volunteers are distributed along the y-axis and the ARF patients the x-axis, thus separating the two groups 90 degrees apart. The CRF patients are scattered away from both x-, and y-axis. This 2-dimensional approach is thought to be very useful for the differential diagnosis of ARF suggesting Udpase as a new member of the marker enzymes of renal disease.