According to the concept of alteration in structure and function to meet the needs of organism, the kidney function develops rapidly after the delivery. Until 2 years of age, however, there are still functional and anatomical immaturities in the neonatal Kidney. The rates of glomerular filtration in the neonates are only 30~50% of those observed in adults. The tubules are even more immature than glomeruli in the neonates. In the infant juxtamedullary and medullary structure are more highly developed than cortex, so that diluting capacity is comparable with that observed in the adult. To observe an aspect of the neonatal kidney function, 24 hour urinary excretion of creatinine, phosphorus, Na, K, Cl, nitrogen were measured in 28 normal male newborns with following results. According to the facts already described it seems valuable to observe the urinary excretory patterns during the neonatal period. 1. Creatinine average: 5.4+/-2.6mg/kg/day 2. Phosphorus average: 6.8mg/day 3. Sodium and Potassium average: 1.0mEq/day Chloride average: 0.7mEq/day 4. Nitogen average: 46.1mg/kg/day.