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Smooth muscle antibody at titres of 1/10 or more was found in 54 (67·5%) out of 80 patients with malignant disease and in 9 (20%) out of 46 controls. The incidence of S.M. antibody ranged from 18/30 (60%) in malignant melanoma to 7/8 (83%) in carcinoma of the ovary. The presence of this antibody is possibly related to changes in the malignant cell membrane. A new antibody directed at an antigen presumed to be located in bile canaliculi among other sites is described.

In 39 unselected patients with acute infective hepatitis diagnosed on clinical, epidemiological, and pathological findings, smooth muscle (S.M.) antibody was found in 87% and hepatitis-associated antigen in 33%. The incidence of S.M. antibody was highest during the first month after the onset of symptoms, and the antibody was preponderantly IgM at this stage. S.M. antibody and hepatitis-associated antigen occurred independently, and unlike hepatitis-associated antigen, which was strongly associated with possible parenteral exposure to infection, the incidence of S.M. antibody was not related to the presumed mode of exposure. It is concluded that production of S.M. antibody is more directly related to liver cell damage than to the presence of hepatitis-associated antigen in the serum.