One of the major metabolites, R-416(3'alpha-OH), of pravastatin sodium(PV, 6'beta-OH), and a minor metabolite, R-418 (6'alpha-OH), were produced in rat liver cytosol in the presence of adenosine 3'-phosphate 5'-phosphosulfate as a cofactor. The reactions were inhibited by the inhibitors for sulfotransferases, and 18OH was introduced to the 3'alpha- and 6'alpha-positions of R-416 and R-418, respectively, by incubation with H2 18O. These results strongly suggested that PV was metabolically activated by sulfation at the 6'beta-hydroxy group by sulfotransferases, followed by nucleophilic attack of hydroxy anions at the 3'alpha- or 6'alpha-position, to give R-416 or R-418, respectively.