There is controversy on whether both primary and secondary pipe smokers do inhale tobacco smoke. We studied inhalation of tobacco smoke in 6 primary and 6 secondary pipe smokers and compared it with that in 20 cigarette smokers and 11 never smokers. Respiratory movements were assessed with inductive plethysmography, nasal flow through measurements of nasal pressure, oral flow with an oral thermistor, puffing through pressure measurements in the cigarette holder or the pipe, and upper airways by fluoroscopy. In all pipe smokers except 1, breathing and smoking appeared as independent activities. The former was exclusively nasal, whereas the latter was exclusively oral. Smoke was sucked and puffed by a to-and-fro movement of the tongue sliding along the soft palate. The oropharyngeal isthmus was closed (or only intermittently opened) by the apposition of the soft palate and the tongue, thus preventing overt inhalation of smoke. In most cigarette smokers, smoking interfered with the breathing route. Once smoke was sucked into the mouth, the oropharyngeal isthmus opened and inspiration proceeded through both mouth (with inhalation of smoke) and nose. Cigarette smoking interfered also with the evenness of ventilation. Never smokers avoided inhalation by oropharyngeal closure followed by oral expiration. We conclude that the oropharyngeal isthmus is the essential gate controlling smoke inhalation. Most secondary pipe smokers are able to change their smoking pattern and avoid overt inhalation when switching from cigarette to pipe smoking. The inhalation pattern appears to be acquired in the course of the smoking history.