A series of phenyl-substituted derivatives of the "minimal" DNA-intercalating agent N-[2-(dimethylamino)-ethyl]-2-phenylquinoline-8-carboxamide (1) have been synthesized and evaluated for in vivo antitumor activity, in a continuing search for active compounds of this class with the lowest possible DNA association constants. Substitution on the 2'-position of the phenyl ring gave compounds of lower DNA binding ability that did not intercalate DNA, indicating that it is necessary for the phenyl ring to be essentially coplanar with the quinoline for intercalative binding. An extensive series of 4'-substituted derivatives was evaluated, but there was no overall relationship between biological activity and substituent lipophilic or electronic properties. However, several compounds showed good solid tumor activity, with the 4'-aza derivative 18 being clearly superior to the parent compound, effecting about 50% cures in both leukemia and solid tumor models.