A series of monosubstituted derivatives of the new antitumor agent N-[2-(dimethylamino)ethyl]-9-aminoacridine-4-carboxamide has been prepared, bearing methyl, methoxy, and chloro groups at available acridine positions. The physicochemical properties and antitumor activity of these compounds varied more with the position than with the nature of the substituent groups. The highest levels of both in vitro and in vivo antileukemic activity were shown by 5-substituted derivatives, while 7- and 8-substituted derivatives possessed the highest selectivity toward the HCT-8 human colon carcinoma line compared to the L1210 mouse leukemia line in vitro.