A prospective study of 113 patients with jaundice and 20 patients with unjaundiced cholestasis was carried out to evaluate the value of serum tumour markers, carcinoembryonic antigen (CEA) and monoclonal antibodies CA 50 and CA 242, in the distinction between benign and malignant diseases causing jaundice and/or cholestasis. In the patients with malignant disease (n = 37) the serum values of all tumour markers were significantly higher than in the patients with benign disease (n = 96). The sensitivities of CEA, CA 50 and CA 242 in detecting malignancy were 70.2%, 94.5% and 56.7%, respectively, while the specificities were 57.2%, 33.3% and 77.0%, respectively. Serum alkaline phosphatase and bilirubin levels had a high positive correlation with CA 50, and CA 242 correlated positively with serum bilirubin levels. No correlation was seen between CEA and alkaline phosphatase or bilirubin levels. The CEA, CA 50 and CA 242 tests may be used as useful complements to other investigative methods in the distinction between benign and malignant causes of jaundice and/or cholestasis. In particular, the rather high specificity of the CA 242 test for malignant diseases seems promising.