Silicone rubber casts were prepared of the nasal, pharyngeal and laryngeal regions of two rats, a rhesus monkey, and three beagle dogs and one for each species selected for detailed measurements. Cross-sections of the casts were made and the area and perimeter of each section measured using an image analyzing computer. Considerable anatomical differences were found between the species. Some of the differences, such as the sharp bend in the nasopharynx of the monkey, could be related to normal posture. One of the main differences was the greater complexity of the turbinate region of the dog as compared to the corresponding area of the monkey.