Quantitation of protein excretion in urine is used for diagnostic and prognostic purposes and also to assess the effects of therapy in children. The method in common use is to measure urinary protein in a 24-hour urine sample, which may be time consuming and is often inaccurate. The aim of this study was to determine if the urine protein/creatinine ratio in a single-void urine sample had a high correlation with the quantity of protein in a 24-hour urine specimen. We found that there was an excellent correlation between the protein content of a 24-hour urine excretion and the protein/creatinine ratios in single morning urine samples of 50 patients. We also discovered that a protein/creatinine ratio greater than 4.9 could signify "nephrotic-range" proteinuria, while a ratio less than 2.5 indicated nephritic syndrome or other renal diseases. We concluded that the determination of urinary protein/creatinine concentration ratios in a single morning urine sample under most clinical circumstances, especially in nephrotic syndrome, could replace the measurement of protein excretion in 24-hour urine specimens.