Serum mitochondrial, nuclear and smooth-muscle antibodies were assayed by the immunofluorescence method in a series of 42 patients with intrahepatic cholestasis of pregnancy and a control series of 15 normal pregnant subjects. None of the subjects examined had mitochondrial antibodies, and nuclear antibodies were only found in one patient with intrahepatic cholestasis of pregnancy. Smooth-muscle antibodies were noted altogether in four patients with intrahepatic cholestasis of pregnancy, in three at a titre of 1 : 40 and in one at 1 : 80; in two controls at titres of 1 : 20, and in two at 1 : 40. In the differential diagnosis of intrahepatic cholestasis of pregnancy the smooth-muscle antibodies particularly may be helpful in differentiating viral hepatitis and intrahepatic cholestasis of pregnancy.