Chromosomal evolution was examined in a long-term cell culture derived from Macaca mulatta eye tissue. In addition to the ‘marked’ chromosome that characterizes the rhesus karyotype, other chromosomes that may have originated from it by inversions and translocations were identified at each subculture sampled. Our observations do not warrant the conclusion that all the achromatically distinguished chromosomes observed were ‘marked’ rather than ‘marked’ chromosomes; some, however, resembled the ‘marked’ chromosomes found in Aotus and Cercopithecus.