We immunohistochemically analyzed the expression of double-stranded RNA-dependent protein kinase (PKR) using a monoclonal antibody, 71/10, Test samples included 64 human liver biopsies and 25 liver sections of rats inoculated with diethylnitrosamine, The PKR signals in human fatty livers and normal rat livers were minimum. Scoring signal intensity from 0-4, the average stores of chronic active (14 cases) and chronic persistent (6 cases) hepatitis associated with hepatitis virus C (HCV) were 2.8 and 2.0, respectively (P = 0.038), The stained cells were significantly more abundant in the periportal than centrilobular regions for both chronic active and persistent hepatitis (P < 0.001 each). The average score of liver cirrhosis associated with HCV was 1.9, Those scores of well-, moderately, and poorly differentiated hepatocellular carcinomas associated with HCV were 3.4, 2.1, and 0.3, respectively (P < 0.001 for each pair), Those scores of well- and poorly differentiated carcinomas associated with hepatitis virus B were 2.3 and 0.0, respectively (P < 0.001). The average score of rat carcinomas induced by diethylnitrosamine was 1.9. Morphologically, nuclei of the vast majority of PKR-positive cells looked not apoptotic, The ratio of PKR-positive cells to apoptotic cells by terminal transferase-mediated dUTP nick end labeling method was approximately 20 in hepatitis, and over 100 in well-differentiated carcinoma.