A comparative study of the karyotypes of eight Xenopus species and subspecies possessing a diploid number of 36 chromosomes (X.l. laevis, X.l. petersi, X.l. victorianus, X. borealis, X. gilli, X. fraseri, and X. clivii) was performed. Karyotypes based on the morphology and size of chromosomes differ only by the type and position of secondary constrictions. Some of these constrictions are nucleolar organizers, recognizable by mitotic chromosomal association. By comparing the chromosomes bearing secondary constrictions, an attempt is made to establish the cytotaxonomic relationships. The close relationship between the subspecies X.l. laevis, X.l. petersi, and X.l. victorianus is confirmed; X. borealis, however, is a separate species much nearer to X. muelleri. The karyotype of X. gilli is interpreted as being intermediate to these two groups. X. clivii could be regarded as a species close to the group of X. muelleri. X. fraseri, having a particular type of secondary constriction, is systematically more distant.