In the course of our screening program for free radical scavenging substances from microorganisms, which are expected to be useful as therapeutic reagents for myocardial and cerebral ischemia1)2), atherosclerosis3) and inflammation4), we have isolated a novel substance named carazostatin from the culture of streptomycete. Carazostatin has shown a strong inhibitory activity against lipid peroxidation induced by free radicals in rat brain homogenate.