In many clinical conditions the nutritional support of patients is inadequate to meet energy, and by extension, protein requirements. The consequence of these semi-starvation regimens are varying degrees of nutritional depletion whose extent is difficult to assess with present techniques. The use of simple anthropometric measurements such as triceps skinfold and arm muscle circumference combined with serum protein levels (albumin and transferrin) not only allow clinical definition of the spectrum of adult malnutrition analogous to the pediatric states of marasmus and kwashiorkor, but individually reflect the state of the major energy stores....fat, skeletal muscle protein, and visceral protein. The purpose of these studies is to survey the nutritional status of patients in a variety of hospital environments, and to develop more sensitive and functional measures of protein depletion, such as adaptation of the creatinine height index to adults and assessment of the host defense system in adult malnutrition (B and T lymphocyte number and function, leukocyte function, and complement levels and activity). A second series of studies will attempt to manipulate the semi-starved state by dietary means so as to minimize the contribution of endogenous protein to energy needs. In contrast to routine protein-sparing therapy with small amounts of carbohydrate, modification of a total fast with small amounts of protein allows better nitrogen economy. Protein-sparing, modified fast will be applied to treatment of other adolescent obese and adult onset obese diabetics, and to minimize the catabolic response to clinically controlled infection (yellow fever vaccine).