A proportion of patients with primary biliary cirrhosis (PBC) develop the CREST variant of systemic sclerosis (SSc) and in these individuals antimitochondrial antibodies (AMA) and anticentromere antibodies (ACA) coexist. Immunological cross-reactivity between mitochondrial and centromere-associated antigens might account for the clinical and serological overlap between these conditions. Therefore, antibodies were affinity purified from the 70 kD polypeptide corresponding to the E2 component of the pyruvate dehydrogenase complex (PDHC) and from CENP-C, a 140 kD centromere-associated protein, to examine this possibility. Although the purified antibodies reacted with their corresponding antigens, no evidence of shared determinants between the 70 kD protein and CENP-C could be detected whether the antibodies were prepared from monospecific sera or from sera containing both AMA and ACA. Therefore, AMA and ACA present discrete autoantibody populations which may coexist in the same patient and may influence the clinical picture but have both structural and immunologically independent antigenic targets.