The review chapter of pulmonary function assessment in small mammals first discusses basic principles and methods such as assessment of various pressures, volumes and flows. The three types of plethysmographs (pressure, flow and barometric) used by animal physiologists are evaluated with special reference to frequency and phase response. A review of ventilatory measurements, usually obtained in unanesthetized animals, is presented. Topics discussed in this section include: anesthesia, restraint, sensory irritation, pulmonary mechanics, airway reactivity, double plethysmography and control of ventilation.