The activity of a novel Ca2+-dependent protease in preneoplastic and neoplastic tissues of male Fisher 344 rat liver was examined during experimental liver carcinogenesis. This protease activity is significantly high in hyperplastic nodules and hepatocellular carcinomas which were induced by the method of Solt and Farber. Taken together with our previous report on the promoter-specific induction of this protease, the results suggest the possible importance of this protease in the promotion stage of liver carcinogenesis.