alpha 1-Antichymotrypsin (ACT) and alpha 1-antitrypsin (AAT) are two closely related antineutrophil proteinase inhibitors. Whereas AAT deficiency is clearly linked to liver disease, an association between liver disease and partial ACT deficiency has not been established. In a previous study we noted an increased prevalence of liver abnormalities among subjects with heterozygous ACT deficiency. To study a possible association between partial ACT deficiency and liver disease, we screened 316 consecutive patients with biopsy-verified liver disease for partial ACT deficiency and compared the prevalence with that of an unselected adult population in a case-control study. In all, 9 of 316 patients had partial ACT deficiency, which is more than expected (prevalence ratio (PR), 2.46 (1.15-5.27), P less than 0.05). The prevalence of partial ACT deficiency was highest in the chronic active hepatitis (5 of 40; PR, 12.0 (5.33-27.0] and the cryptogenic cirrhosis (3 of 24; PR, 12.0 (4.38-32.9] subgroups. In the chronic active hepatitis subgroup two patients (PR, 8.16 (2.25-29.5] were ACT deficiency heterozygotes, thus partly explaining the high prevalence of partial ACT deficiency among patients with chronic liver disease. The majority (6 of 9) of the patients with partial ACT deficiency lacked autoimmune and viral markers and were thus cryptogenic. The present findings show that partial ACT deficiency and chronic cryptogenic liver disease are associated. To some extent (the true magnitude of which is at present unknown) partial ACT deficiency is caused by a rare trait, heterozygous ACT deficiency, which in parallel with heterozygous alpha 1-antitrypsin deficiency (PiMZ) also seems to be associated with chronic cryptogenic liver disease.