Delayed hypersensitivity responses to recall antigens were measured in 125 surgical patients referred for nutritional assessment and support. On initial testing 57 patients were skin test positive and 68 were anergic each of these patient groups being closely matched in terms of surgical conditions. There was a mortality of 4 in the skin test positive group and 26 in the anergic group. The anergic patients were significantly older and in biochemical and anthropometric terms were in poorer nutritional status than the skin test positive group. Of 33 anergic patients who were repeat tested, 15 remained anergic and 18 converted to a positive response. Conversion from anergy to a positive response was not associated with changes in the measured indices of nutritional status and did not improve clinical outcome. The value of repeat skin testing is therefore in doubt.