To evaluate the usefulness of a single voided urine protein/creatinine ratio in quantitation of proteinuria, correlations between protien/creatinine ratio in a single voided urine and the amount of 4hr urine protein were studied in 43 patie nts with variable amount of abnormal proteinuria. The results were as follows: 1) Correlation between protein/creatinine ratio in a random single voided urine and amount of 24 hr urine protein shows the close correlation in all p atients regardless of the time of voiding(r= 0. 82, p<0. 001). 2) During the daytime, when active physical activities are performed, urinary protein/creatin- ine ratio in a single voided urine have highest correlation with 24hr urine protein. 3) The slopes of protein/creatinine ratio as a function of 24 hr urine protein excretion were ne- ar ly 1.0 during daytime and decreased during the night. 4) Protein/creatinine ratio as a function of 24 hr urine protein excretion were influenced by total amount of daily creatinine excretion. 5) After the treatment of nephrotic syndrome with steroid, protein/creatinine ratio was decrea- sed with simultaneous decrease of 24 hr urine protein. Above results suggest that the ratio of urinary protein to creatinine concentration of a random single voided urine sample, especially during da- ytime activity, can be used as index for quanti- tating urinar y protein.