The morphology of the nasal fossa and turbinate system was studied in two species of prosimian primates (Tupaia glis and Nycticebus coucang) and two species of anthropoid apes (Macaca fascicularis and Hylobates agilis). This comparative study revealed that there is a reduction in the number of turbinates in the anthropoid apes together with a relative reduction in the length of the nasal cavity. The nasal fossa height, however, increased with a concomittant decrease in its width.