Using ELISA methods, 54 sera from chronic active hepatitis (CAH) patients displaying high levels of anti-smooth muscle antibodies (SMA) and 18 sera from primary biliary cirrhosis (PBC) patients with high levels of anti-M2 antibodies were examined for the presence of high antibody levels against actin, tubulin, myosin, tropomyosin, troponin, vimentin and desmin. Our results showed that: (i) in CAH with high SMA activity, increased antibody levels were found in 51.9% of sera for actin, 31.5% for myosin, 35.2% for tubulin, 34.0% for tropomyosin, 11.3% for troponin, 22.6% for vimentin and 43.4% for desmin, compared with natural antibody levels in 21 normal sera; (ii) Similar high levels of these antibodies were found in the case of PBC; (iii) in most cases, sera simultaneously bound to several antigens of the panel; and (iv) approximately 26% of the CAH sera were found to be negative with the seven antigens examined while 22% were reacted with a cytoskeleton protein (CP) other than actin. These results indicate that current opinion associating SMA with anti-actin activity in CAH is confirmed for only 50% of cases and that although a good correlation between SMA and anti-CP antibodies can be obtained, there is still a significant percentage of SMA for which the putative antigen recognized needs to be determined.