The subjects were all Chinese male adults. The average age, body weight and height were 37.9 (24-44) yr, 64.3 (51.5-74.0) kg and 173 (157-180) cm respectively in the first group, and 30.2 (24-41) yr, 67.7 (56.5-70.0) kg and 171 (170-176) cm respectively in the second group.The subjects in the first group were studied for 70 days for the N balance response at graded protein intakes of 0.42, 0.60, 0.73, 0.90 and 1.05 g/kg /day on Chinese mixed diet, during 5 experimental periods respectively. Each period took ten days preceded by one day of low protein diet, and was followed by three days of free choice diet The sequence of protein intakes during the study was 0.60, 0.73, 0.42, 0.90 and 1.05 g/kg/day. Six subjects in the second group were given a mixed diet ata protein level of 0.93 (0.91-0.94) g/kg/day for three months.In the N balance data of the first group, all subjects were in negative balance at protein intake of 0.42, 0.60 and 0.73 g/kg/day and all in positive N balance at 1.05 g/kg/day. Most of the subjects were in positive N balance at 0.90 g/kg/day. The linear regression analysis of N balance response of individual subject is that the intercept at zero balance of individuals ranged from 129.4-192.5 mg N/kg/day with the mean of the group of 147.7? 18.6mg N/kg/day or 0.92?0.12 g protein/kg/day. The five of the six subjects in the second group were in positive N balance, when on a mixed diet of 0.93 ?0.02 g protein/kg/day for three months.The results obtained indicated the mean protein requirement of these subjects based on the linear regression analysis of N balance response of individuals was 147.7 ? 18.6 mg N/kg/day or 0.92?0.12 g protein/kg/day. If 97.5% is to be covered, the safe level of protein intake should be 1.16 g protein/ kg/day.