We investigated the specificities and characteristics of anti-cytoskeleton antibodies in 13 anti-smooth muscle antibody (ASMA)-positive patients with chronic liver disease C (CLD-C), and compared them with those in 7 ASMA-positive patients with autoimmune hepatitis (AIH), and 6 ASMA-positive patients with chronic liver disease B (CLD-B). Anti-microfilaments (anti-MF) were found not only in 6/7 AIH patients (85.7%), but also in 8/13 CLD-C patients (61.5%) with a relatively high incidence, when compared with 1/6 CLD-B patients (16.7%), while, there was no significant difference in the incidence of anti-intermediate filaments (anti-IMF), especially anti-IMF IgM, among these patient groups. Among the patients with CLD-C, the mean levels of serum gammaglobulin and IgG in the anti-MF-positive patients were 2.46 +/- 1.03 g/dl and 3277 +/- 1089 mg/dl, respectively, which were higher than those in the anti-MF-negative patients (1.60 +/- 0.53 g/dl, 2245 +/- 610 mg/dl) and those in the patients with CLD-B (1.60 +/- 0.57 g/dl, 2192 +/- 339 mg/dl). Furthermore, 4 of the 8 anti-MF-positive patients with CLD-C satisfied the serological criteria for the diagnosis of AIH. These findings suggest that autoimmune mechanisms might be involved in the pathogenesis of anti-MF-positive CLD-C, and that anti-MF might be used as a marker.