A study was conducted to determine the protein requirements of normal young male subjects fed a model Mexican rural diet. The multiple-level nitrogen-balance technique was used in eight subjects; three of them were also studied when ingesting a milk diet. The mean requirements for the rural and milk diets were 112 and 105 mg N/kg body weight, respectively; accordingly, the amount of protein needed to cover the requirements of 97.5% of the population, calculated by method 3 of Rand, Scrimshaw and Young were 136 mg N/kg body weight for the rural diet, and 122 mg N/kg body weight for the milk diet. Interestingly, the NPU and the digestibility of the rural diet increased as the intake approached the requirement level.