A total of 489 consecutive 24-hour urine collections from 162 patients were analyzed for creatinine excretion. The 24-hour creatinine excretion increased with the urine volume. Creatinine excretions in 24-hour urine collections were not statistically different between in- and out-patients. The results indicate that the mean urine creatinine per 24 hours is 1.08 g for 24-hour urine volumes between 500 and 1500 ml. For urine volumes > 1500 ml it is 1.22 g. For 24-hour urine volumes < 500 ml, the mean creatinine is 0.63 g.