THE ROLE of chromosome cytology in primate evolution is reviewed and discussed thoroughly by Chu and Bender (1961 and in press). In our study the data on primates of the above mentioned authors and others (Young et al., I960; Chiarelli, 1961; Hamerton et al., 1961) have been supplemented with chromosome studies of some species of the Hominoidea which have never been studied or for which the previous data are incomplete. We repeated some species because it was thought important that the material all be processed in the same laboratory under similar technical conditions. This should increase the reliability of comparative studies.