Replication patterns after 5-bromodeoxyuridine incorporation are analyzed in chromosomes of four species of the genus Cebus (C. capucinus, C. albifrons, C. appella, and C. nigrivittatus). They are compared with those of man, taking as reference the banding analyses previously described. It was found that the high degree of conservation of chromosome structures between Cebus and man was accompanied by conservation of the DNA-replication sequence of the bands. It is assumed that this conservation during the course of evolution may apply to other mammals. Thus, replication patterns may be useful for ensuring interspecific comparisons. The only detected difference concerns late-replicating X chromosomes from normal female cells: The predominant lymphocyte pattern described in man is rare in Cebus, in which the usual lymphocyte pattern corresponds to that of human fibroblasts or to the minor human lymphocyte pattern.