The impact of malnutrition on survival in AIDS was evaluated by examining the magnitude of body-cell-mass depletion as a function of time from death. Body cell mass was estimated as total body-potassium content and determined by whole-body counting. There was progressive depletion of body cell mass as patients neared death. The extrapolated and observed values for body cell mass at death were 54% of normal. Body weight had a similar relationship to death, with a projected body weight at death of 66% of ideal. We conclude that death from wasting in AIDS is related to the magnitude of tissue depletion and is independent of the underlying cause of wasting. The degree of wasting seen in this study is similar to historical reports of semistarvation, with or without associated infections. This observation suggests that successful attempts to maintain body mass could prolong survival in patients with AIDS.