In 182 critically ill patients, after admission delayed hyersensitivity skin testing have been systematically performed with 3 antigens (tuberculin, candidin, varidase). Mortality in anergic patients was 55% while it dropped to 19% when at least one response was positive. A highly significant relationship was found between anergy and mortality (p less than 10(-5)) whether death was related to sepsis (p less than 10(-4)) or not (p less than 0.02). In patients with major sepsis, anergy was more frequent (38%) than in non septic patients (21%) (p less than 0.01). In 69 patients skin testing with phytohemagglutinin was performed. Seven out of 8 unresponsive patients were anergic and 5 died. The results suggest that in critically ill patients cellular immunity skin testing may early select high risk patients exposed to septic complication. In these patients several important measures should be promptly taken including superinfections prevention, adapted nutritional intake and septic focus eradication.