A series of 9-anilinoacridine derivatives substituted in the anilino ring with a variety of phosphoramide and related substitutents has been prepared, and the antitumor activity has been evaluated both in vivo and in vitro against the L1210 or P-388 mouse leukemia systems. The DNA-binding properties were measured using the ethidium displacement method, and the structural requirements for strong binding were found to differ from those for antileukemic activity. For high biological activity a marked preference for oxygen-containing substituents on the phosphorus atom was noted, while for high DNA binding a requirement for nitrogen-containing or cyclized substituents was observed. The most active congeners, as assayed in both in vitro and in vivo systems, were comparable in activity to the clinically utilized anilinoacridine derivative N-[4'-(9-acridinylamino)-3'-methoxyphenyl]methanesulfonamide (m-AMSA, amsacrine).