Cyclic voltammetry and in situ FT IR spectroelectrochemistry (SEC) were used to monitor the change of the peroxide group of artemisinin in the presence of hemin. On the glassy carbon electrode, artemisinin alone was reduced at potentials more negative than -1.0 V in CH2Cl2; no well-defined reduction peak was observed. In the presence of a concentration of hemin as low as 10(-7) M, artemisinin can be irreversibly reduced via hemin catalysis. In situ FT IR SEC experiments confirmed the catalysis of hemin for the reduction of artemisinin. The changes of IR spectra for the peroxide bond of artemisinin at 1114 cm(-1) clearly showed hemin inducing the cathodic cleavage of the peroxide bond. These results might contribute to an understanding of the antimalarial action of artemisinin.