The cttl+ gene in Schizosaccharomyces pombe encoeds a catalse responsible for H2O2-resistance of this organism as judged by the H2O2-sensitive phenotype of the ctt1Δ mutant. In this study, we investigated the subcellular localization of the Ctt1 gene product. In wild type cells catalase activity was detected in the organelle fraction as well as in the cytosol. The ctt1Δ mutant contained no catalase activity, indicating that both cytosolic and organellar catalases are the products of a single ctt1+ gene. Western bolt analysis revealed two catalase bands, both of which disappeared in the ctt1Δ mutant. The major, fastermigrating band existed in the cytosol whereas the monor, slower-migrating band appeared to be located in organelles, most likely in peroxisomes. These results suggest that the ctt1+ gene product targeted to the peroxisome is a modified form of the one in the cytosol.