In vitro antitumor activities of 13 saframycins, including the potent antitumor component, saframycin A, were determined with the highly sensitive established cell line of L1210 mouse leukemia to investigate structure-activity relationships. Saframycins which lack the alpha-cyanoamine group or the alpha-carbinolamine group exhibited much lower cytotoxic activity than saframycin A. The modification of active saframycins either at the C-14 position on the basic skeleton or at the C-25 position on the side chain with bulky substituents resulted in a decrease in cytotoxic activity. These structure-activity relationships corroborated the proposed major mechanism of action for the antitumor activity of saframycin A and supported our proposed model for the saframycin A-DNA adduct.