The banded chromosomes of Harrison’s monkey, Cercopithecus (lhoesti) solarus, and Preuss’ monkey, Cercopithecus (Ihoesti)preussi, were studied for the first time and compared with those of l’Hoest’s monkey, Cercopithecus (lhoesti] Ihoesti; the savannah guenons, Cercopithecus aethiops ssp. and the patas monkey, Cercopithecus (Erythrocebus)patas. The karyotype of C. preussi was identical to that previously reported for C. Ihoesti, and differed by three chromosomal rearrangements from C. solatus. The latter’s next closest cytogenetic affinities were to the savannah guenons and then to C. patas. These data were consistent with the designation of C. solatus as a new species.