The morphology and quantitative features of skulls and teeth of Papio cynocephalus from different parts of Northern Rhodesia and Nyasaland have been studied and compared. A west to east geocline showing increasing size is indicated. Comparison of the material with that of Papio ursinus suggests the possibility that, from the eastern end of its range, the skull size increase in the proposed P. cynocephalus cline is continued to the south by specimens of P. ursinus and to the north by specimens of Papio doguera. Some problems of taxonomy in the genus Papio are discussed.