Two hundred and twenty-six patients suspected of having liver disease were examined clinically, by a liver biopsy and laboratory test, according to a prospective scheme. Blood samples obtained just before the liver biopsy were coded and subsequently examined blindly, using the complement fixation test (CFT). The antigens were influenza A and B viruses, parainfluenza 1, 2, and 3, respiratory syncytial viruses, varicella, morbilli, cytomegalo and herpes simplex viruses. The sera were also examined by the CFT against Mycoplasma pneumoniae antigen. Antibodies against rubella virus were determined in a haemolysis-in-gel test. HBsAg and HBsAb were determined by a staphylococcal radioimmunoassay, and sera from patients with chronic active hepatitis (CAH) and chronic persistent hepatitis (CPH) were also examined for antibodies against hepatitis A virus by radioimmunoassay. Highly significant antibody titres against morbilli virus were found in patients with CAH and CPH. Patients with CPH or liver cirrhosis also had significantly higher titres against rubella virus than other groups. Some patients with liver granulomas had high titres against rubella virus. Only in one patient with CAH was a positive test for HBsAg found, and in one a positive test for HBsAb. Seven patients in the CAH and CPH groups had very high titres against both rubella and morbilli viruses.