Clinical efficacy of doxorubicin is compromised due to free radical generation leading to cardiac toxicity. Oil-soluble organosulfur compounds, diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS) and dipropyl disulfide (DPDS), present in garlic were examined for their antiperoxidant effects. DADS inhibited liver microsomal lipid peroxidation induced by NADPH, ascorbate and doxorubicin. DAS, DPS and DPDS were ineffective inhibitors of liver microsomal lipid peroxidation. DADS could be used in combination with doxorubicin to protect oxidative injuries to improve the clinical efficacy of doxorubicin.