Three physiologic scoring systems, the Physiologic Stability Index (PSI), the Pediatric Risk of Mortality (PRISM), the Acute Physiologic Score for Children (APSC), and the Therapeutic Intervention Scoring System (TISS) were applied to 32 critically ill infants and children with acute renal failure or multiple organ system failure undergoing continuous extracorporeal renal support. APSC was developed from the Apache II score. It describes 6 organ systems with 14 variables. PSI describes 7 organ systems with 34 variables, PRISM 5 organ systems with 14 variables. Simultaneously, the TISS was recorded at admission, 24, 48, 96 and 144 h later. All physiologic scores showed significant differences between survivors (S) (n = 18) and nonsurvivors (NS) (n = 14) from admission on. The highest significance was obtained with the APSC (admission score: S: 17.8 +/- 7.4 vs. 27.1 +/- 11.4 NS; p = 0.01; day 4: S: 10.3 +/- 6.1 vs. 26.1 +/- 10.8 NS; p = 0.0001). No significant differences in TISS and in the number of organ system failure were observed during the first 4 days of intensive care.