Airflow patterns in the nasal passages influence the distribution of air-pollutant-induced lesions in the airway mucosa. Little is known about airflow characteristics of the complex nasopharyngeal airway of man and experimental animals. Airflow characteristics in the nasopharyngeal airways of an adult male baboon (13.9 kg) were investigated with thermistor probes and the findings compared with flow visualization, using a cine-photographic technique. A clear, acrylic, hollow cast of a baboon nose was made, and thermistor probes were inserted to record air velocity in the cast lumen using a wind tunnel to propel air through the cast. An identical cast was studied by passing water through the cast and using pulses of blue dye to reveal flow patterns, and then velocities and flow patterns were determined from cine film with an analytical projector. Flow rates showed good correlations between the two methods, whereas cine-photography revealed areas of turbulence and vortex-like flow. These results suggest that water flow may provide useful information in complex airways where airflow cannot be determined.