New modifications of 10-[[3-(diethylamino)propyl]amino]-6-methyl-5H-pyrido[3',4':4,5]pyrrolo[2,3-g]i sisoquinoline (1b) and 1-[[3-(diethylamino)propyl]amino]-9-methoxy-5,11-dimethyl-6H-pyrido[4,3-b]carba zole (4b), which display important antitumor properties, were performed either on the side chain or on the intercalating heterocycle. Side chains were introduced by direct substitution of the corresponding chloro derivatives and 6-N-methyl-9-hydroxypyrido[4,3-b]carbazoles analogues were prepared via 9-O-benzoyl-1-chloroellipticines. Evaluation of all new compounds shows no significant increase of in vitro cytotoxicity and percent ILS on the L1210 leukemia system by comparison with the model compounds 1b and 4b.