The assumption that the respiratory system behaves with 2 df of motion in healthy persons allows calibration of respiratory inductive plethysmography (RIP) with spirometry (SP). To ascertain whether RIP could be calibrated by the same assumption in patients with lung disease, even though at least 3 df of motion are visualized (ie, upper and lower rib cage and upper and lower abdomen move out of phase), RIP was calibrated by a two-position calibration procedure and validated satisfactorily by simultaneous SP in the erect, semirecumbent, supine, and lateral decubitus positions. In lung disease, the contribution to tidal volume of regions moving independently of the combined rib cage and abdominal movements either is small or remains relatively constant with change of body posture. For clinical monitoring of the resting breathing pattern where patient movements cannot be restricted, respiratory inductive plethysmography can serve as a reliable semiquantitative, noninvasive ventilatory monitoring device.