Eighty-one patients with HCV positive chronic active hepatitis (CAH) were studied to correlate, in multivariate regression analysis, liver tests with the histological activity index (HAI). The median HAI value (9.4) divided the patients into two groups; 44 under the 9.4 value (moderate CAH) and 37 above (severe CAH). Multiple regression improved the significance of nine biochemical parameters related to HAI in univariate analysis, and backward stepwise analysis identified the combination of alanine-aminotransferase (ALT), gammaglobulins (gamma GL), gammaglutamyl transpeptidase (gamma GT) and prolyl-hydroxylase (PH) as the best relationship with HAI (R = 0.520, p < 0.0001). A biochemical activity index (BAI) calculated as: 2.304 + ALT x 0.013 + gamma GL x 1.76 + gamma GT x 0.008 + PH x 0.012 showed the higher significant difference between moderate (7.7 +/- 1.3) and severe (12.2 +/- 2) CAH (p < 0.0001). These results suggest that this BAI could be a pointer for checking activity of chronic liver diseases.