A Histology Activity Index has been developed which generates a numerical score for liver biopsy specimens obtained from patients with asymptomatic chronic active hepatitis. Biopsies are graded in four categories: periportal necrosis, intralobular necrosis, portal inflammation, and fibrosis. Under code, three pathologists and three hepatologists evaluated 14 liver biopsy specimens obtained from five patients with asymptomatic chronic active hepatitis. Good correlation was seen between severity of liver biopsy lesions as judged by conventional histological descriptions and Histology Activity Index scores. Significant differences in Histology Activity Index score occurred in only 2 of 28 duplicate scorings of biopsy specimens by two observers. This system provides definitive endpoints for statistical analysis of serial changes in liver histology and offers an alternative to the use of conventional pathological descriptions in following the natural history and treatment responses of asymptomatic chronic active hepatitis.