A prospective study of delayed hypersensitivity was carried out in jaundiced patients. One hundred and nineteen subjects were studied. Fifty-nine were controls and sixty were patients with pancreatobiliary pathology and biliary tract obstruction. A Multitest technique was used to evaluate the delayed hypersensitivity response, classifying the subject into one of three groups: immunocompetent, relatively anergic and anergic. In the control group, 76 per cent of the subjects were immunocompetent as opposed to 17 per cent of the patients (P less than 0.001). Ten per cent of the control subjects and fifty-five per cent of the patients presented anergy (P less than 0.001). Amongst the patients no difference could be found in the index of anergy between malignant or benign pathology. A greater incidence of postoperative septic complications in anergic and relatively anergic patients was found. Our study indicates a relationship between jaundice and anergy.