This paper has reviewed changes in body composition and protein metabolism that are associated with aging. Body protein mass decreases. Rates of both muscle and whole-body protein turnover/kg body weight decrease, and the percentage of turnover contributed by muscle to whole-body turnover decreases with age. Total plasma proteins, albumin, prealbumin, transferrin and ceruloplasmin levels decline with age, and, in the case of albumin levels, the decline continues when young-old are compared with old-old. Protein requirement of the elderly appears to have been underestimated by the factorial method. Nitrogen balance studies indicate a minimum of 0.7 g protein/kg/day in one study. Several studies show 0.8 g, whereas other studies show negative nitrogen balance at this level. The recommended protein intake is 1 g protein/kg/day, and 12-14% of total calories should be provided by protein. The few nitrogen balance studies that attempted to determine essential amino acid requirements are limited and contradictory.