Freeradical scavenging activities of various carbazole compounds, carazostatin, carbazomycin B and their chemically modified derivatives were studied in vitro and ex vivo. Among these compounds, carazostatin, which was isolated as a freeradicalscavengerfrom the culture of Streptomyces chromofuscus, showed the most potent inhibitory activity against lipid peroxidation of rat brain homogenate in