Epimerization and hydrolysis of etoposide and its analogues involving aglycons were examined in alkaline aqueous solution. The trans-lactone compounds such as etoposide were epimerized to the cis-lactone compounds such as picroetoposide, but not hydrolyzed to trans-hydroxy acid derivatives. The cis-lactone compounds were susceptible to the hydrolysis of the lactone ring. The epimerization was accelerated by the presence of the sugar substituent at position 4 and of the methoxy group at position 4'. The epimerization was also affected by the configuration of the hydroxyl group at position 4. The hydrolysis rate of the cis-lactone was decreased by the sugar substituent at position 4, and increased by the methoxy group at position 4'. The configuration of the hydroxyl group at position 4 had no effect. The nuclear magnetic resonance data suggest that the structure of etoposide is more strained and less than that of the aglycon. The acceleration of the epimerization by the sugar substituent may be ascribed to the decrease in the stability of the trans-lactone by glycosidation. The decrease of hydrolysis rate owing to glycosidation may be explained in terms of the steric handrance of the bulky sugar substituent.