A study of the Q (quinacrine fluorescence) and G (Giemsa) banding patterns of the chromosomes of Pan troglodytes and Gorilla gorilla gorilla shows that they are almost identical. The differences include a pericentric inversion in pairs 5, 9, 19 and the X-chromosome, a possible translocation between pairs 7 and 17 of gorilla and a deletion of part of the long arms of the Y-chromosome in the chimpanzee. Several species of the genera Macaca, Papio and Cercocebus have the same karyotype and identical banding patterns. This suggests that speciation in this group may have taken place on purely genic grounds, without, involving any karyological changes. © 1973.