Plasma proteins, triglyceridemia, body composition and delayed hypersensitivity were determined in 154 critically ill patients after admission. Plasma proteins levels were significantly increased in patients that were subsequently discharged vs. those that died: albumin: 33 +/- 6 g/l vs 28 +/- 6 g/l (p < 10(-6)); transferrin 2,18 +/- 0,65 g/l vs. 1,54 +/0 0,55 g/l (p < 10(-7)); prealbumin: 14,32 +/- 7,79 mg/100 ml vs. 7,28 +/-5,36 mg/100 ml (p < 10(-7)) and triglyceridemia was decreased: 1,07 +/- 0,38 g/l vs. 1,66 +/- 1,12 g/l (p not equal to 10(-3)). Body weight, fat weight and lead body mass were not correlated to subsequent mortality. Muscle cell mass was decreased (-17%, p < 10(-2)) and extracellular water was increased (+14%, p < 10(-4)), in patients who subsequently died. Total body water and visceral cell mass did not change. Initial anergy (tested with 3 antigens: candidin, tuberculin, varidase) did correlate with mortality: 35/62 died when delayed hypersensitivity was negative vs. 13/71 when it was positive (p < 10(-4)). Mortality was associated with decreased total lymphocyte count: 884 +/- 1025 vs. 1270 +/- 870 (p < 0,02) and serum iron: 51 +/- 40 micrograms/100 ml vs. 74 +/- 45 micrograms/100 ml (p < 10(-2)). Sepsis correlated with mortality (p < 10(-3)) and could produce these changes. These results suggest that critically ill paients have a protein-calorie malnutrition syndrom marktly different from that observed in simple starvation. Nutritional therapy must be, in this group of patients, adapted to this concept.