4,4'-(3,7,12,16-Tetramethyl-1,3,5,7,9,11,13,15,17-octadecanonaen-1 ,18-diyl) bis (1-ethylpyridinium) dibromide (Y-18598), a novel carotenoid analog with 1-ethylpyridine rings as terminal groups, was found to be effective against P388 leukemia which was refractory to amphotericin B and retinoic acid used as representatives of polyene-containing drugs. The life span of leukemic mice was increased by 56% over the control following administration of 2.5 mg/kg on days 1-5. Among these polyene-containing compounds, Y-18598 was the most highly cytotoxic to P388 leukemia cells in vitro.