Newly modified-echinomycin such as S-methylated sulfonium perchlorate of echinomycin (1), monosulfoxide (2), disulfoxide (3) and sulfone (4) have been prepared and evaluated for in vitro biological activities of cytotoxicity against P388, B16 and SNU-16 as well as in vivo antitumor activity against murine leukemia P388 and melanoma B16. (C) 1998 Elsevier Science Ltd. All rights reserved.