Grignard addition of 14CH3MgI to methyl ester of 4-keto-4-nortetrahy-droartemisinic acid （3） gave （15-14C） 4-hydroxytetrahydroartemisinic ester （4 α）. 4α was dehydrated with P-toluenesulfonic acid in benzene followed by alkaline hydrolysis to obtain a mixture of dihydroartemisinic acid （5 α） and its isomer （6α）. The mixture was oxidized with OsO4 and N-methylmorpholine-N-oxide to give （15-14C） dihydroartemisilacton （2α） and （15-14C） 3

4-dihydroxyartemisinic acid （7α）. In addition the corresponding 13C and 2H labelled compounds were also prepared.