1. The structures, including stereochemistry, of the two major metabolites of pravastatin sodium in an isolated rat hepatocyte system, i.e. the 4'a alpha-glutathione conjugate (CM-1) and the 3',5'-dihydrodiol (CM-2), were determined by one- and two-dimensional n.m.r. spectroscopy. 2. The structures of two synthetic pravastatin epoxides, possible precursors of the metabolites, were also established. 3. One of the synthetic epoxides, 4'a beta, 5' beta-epoxide was converted to the pravastatin metabolite, 4'a alpha-glutathione conjugate (CM-1) by a rat liver cytosol system and is proposed as the common metabolic intermediate between pravastatin sodium and the metabolites, CM-1 and CM-2.