Respiratory Induction Plethysmography (RespitraceTM) is a recently described method for noninvasive respiratory monitoring in adults. We report here on its calibration and use in 15 infants. Tidal volume, as measured by this method, was compared with the tidal volume integrated from a pneumotachygraph attached to a tightly fitted face mask. The 2 volumes had a correlation greater than 0.85 (p less than 0.001) with a slope between 0.9 and 1.1. The results were similar in both quiet and rapid eye movement sleep demonstrating that the method can accurately follow paradoxical inward rib cage movement. However, the accuracy decreased at respiratory rates above 80 breaths/min. When the minute ventilation was computed over the same sampling interval by both methods, the mean difference was +0.2 +/- 3.4% (+/- 1 SD) in quiet sleep and +0.8 +/- 4.5% in rapid eye movement sleep. We concluded that this is an accurate method of measuring long-term minute ventilation and tidal volume in small infants, provided that both the calibration procedure and measurements are made in the same posture, and the infant's respiratory rate is less than 80 breaths/min.