Solid silicone rubber casts of the nasopharyngeal and laryngeal regions of a human cadaver (child, three years old) and a laboratory primate (baboon, 10 years old) were made and cross-sectional areas were measured in detail. Cross-sectional areas of other species reported in the published literature were used for comparison. In the child's nose cast, the frontal nasal duct, which enters the anterior part of the middle meatus, and the sphenoidal recess were almost absent. The ethmoidal turbinates and the maxillary turbinates were present but were not fully developed. In the baboon nose, the different turbinates were well defined and smooth but of less complex nature. Of the species compared, the baboon's upper airways had the greatest similarity to the human child's. The study shows that for the species investigated and for those from the literature, the cross-sectional area increases from the external nares to the maxilloturbinate region. There is a relatively sudden drop in cross-sectional area about halfway through the nose. The study suggests a functional relationship between nasal structure and cross-sectional area across species. (Copyright (c) 1986 Allan R. Liss, Inc.)