Two patients with characteristic features of CREST syndrome and primary biliary cirrhosis are reported. Sera of both patients contained autoantibodies to centromere and mitochondrial antigens. Immunodiffusion analysis identified the specificities of precipitating antibodies to mitochondria of the first case as anti-M-A and M-C, and of the second case as anti-M-A and M-B antibodies. Simultaneous occurrence of 2 marker antibodies in an individual patient indicates that the 2 patients reported here have CREST syndrome and primary biliary cirrhosis, both of which are considered as a distinct clinical entity.