Total respiratory compliance (Crs) has not previously been measured from the static pressure-volume (P-V) curve during spontaneous breathing in anesthesized infants and children. A single breath test and a volume recruitment maneuver for measuring Crs were applied to 18 infants and children breathing spontaneously during halothane anesthesia in order to determine the usefulness and reliability of these noninvasive tests for measuring static compliance during anesthesia. Crs from the single breath test (Crssb) was determined from the mask pressure plateau (P) during a brief end-inspiratory airway occlusion and the lung volume (V) from the passive expiration following release of the occlusion. Crs from the volume recruitment maneuver (Crsvr) was determined from P and V during a series of expiratory occlusions at progressively higher lung volumes. The P-V curves fit a polynomial curve with the convexity toward the pressure axis in most patients, and Crsvr was the tangent to the curve in the mid-tidal range. The tallest four patients did not show respiratory muscle relaxation during the occlusions with either test, and the single breath test could not be completed in an additional two patients. In the 12 patients (59-89 cm in height) in whom both tests were successful, Crssb correlated with, and was similar to, Crsvr. The intrasubject coefficient of variation was less with the single breath test (9.4 +/- 6.7%) than with the volume recruitment maneuver (15.0 +/- 7.1%). The authors conclude that both tests are simple, reliable, and rapid and give similar results for Crs in spontaneously breathing children (59-89 cm in height) anesthetized with halothane.