Th antiproliferative activity ofN-substituted 2,4-diamino-5-aryl-5,6,7,8,9,10-hexahydrobenzo[b][1,8]naphthyridine-3-carbonitriles was studied. Substituents in the 5- and 7-positions of the naphthyridine ring had strong influences on the activity; in the 1-position, weak influences. Compounds with a C-5 3,4,5-trimethoxyphenyl radical were significantly superior to other derivatives. The influences of other substituents were not precisely established; however, a C-7 substituent played a key role in the manifestation of biological activity.