To define severity of illness objectively and to justify further the need for intensive care, we have analyzed measurable objective data points (indicators) in 226 consecutive critically ill Class IV patients. The indicators include: (1) Pao2 (Fio2, 1.0), (2) platelet count, (3) cardiac index, (4) BUN, 5) creatinine, (6) acute renal failure, (7) peritoneal or hemodialysis, (8) continuous infusion of antiarrhythmia therapy, (9) base deficit greater than 10mEq/liter, (10) state of consciousness, and (11) unexpected cardiac arrest. Most indicators were significantly worse in patients who ultimately died within one year than in patients who survived with a successful recovery. An indicator profile could be derived for each disease process category, since different indicators applied to different diseases. The indicators were not markedly affected by age. Standard discriminate analysis predicted a group of patients who would not survive and documented that acute renal failure was a primary predictor of death.