The effect of protein distribution on nitrogen balance and the plasma aminogram was studied in a 34-month-old male child with propionic acidemia. Protein provided 4.8% of energy of which high biological value protein was given either as a bolus or evenly distributed in three meals per day. Analysis of nitrogen balance including estimated sweat nitrogen losses revealed no major difference between the two diets. No marked differences in the fasting plasma concentrations of essential amino acids were noted with protein distribution. A generalized increase in concentration of all nonessential amino acids except taurine and ornithine was noted when protein was evenly distributed throughout the day. The ratio of nonessential to essential amino acids was higher after even protein distribution than when protein was given as a bolus. The data suggests that a low protein diet (206 mg nitrogen/kg/day) with adequate energy intake used in managing this child with propionic acidemia provided adequate amounts of total nitrogen and essential amino acids for normal growth regardless of protein distribution.