The potential of respiratory inductive plethysmography (RIP) to detect inspiratory flow limitation during sleep was investigated. Sixteen sleep apnoea patients underwent polysomnography. Airflow by a flowmeter attached to a nasal mask, oesophageal and mask pressure were recorded along with calibrated RIP. Presence of inspiratory flow limitation was defined by constant or decreasing flow without pressure dependence throughout significant portions of inspiration, its absence by a linear or mildly alinear pressure:airflow relationship. Based on this standard, three of various computerized RIP derived parameters, with highest performance to detect flow limitation, were identified. They were combined to an inspiratory flow limitation, (IFL)-Index(RIP), which was validated prospectively in another 10 sleep apnoea patients. RIP derived fractional inspiratory time, peak to mean inspiratory flow ratio, and ribcage contribution to tidal volume had the highest accuracy to detect flow limitation (area under the receiver operating characteristic (ROC) curves 0.81, 0.76, 0.76, respectively, 160 comparisons). Prospective validation revealed an area under the ROC curve for the IFL-Index(RIP) to detect flow limitation of 0.89 (95% confidence interval 0.85 to 0.93, 200 comparisons) with sensitivity and specificity at the point of equality of 80%. It is concluded that inspiratory flow limitation may be assessed by computer assisted analysis of respiratory inductive plethysmography derived breathing patterns with clinically acceptable accuracy.