We studied the correspondence between fluctuations of esophageal pressure measured before and after placement of a nasogastric (NG) tube in six normal volunteers. Flow, airway pressure, and esophageal pressure data from at least 20 breaths were recorded in seven ventilatory conditions in two body postures: 0 degree (supine) and 60 degrees (upright). The conditions studied included normal quiet breathing, added resistance, reduced compliance, increased frequency, increased tidal volume, continuous positive airway pressure, and volume-cycled ventilation with positive pressure. During recording with the NG tube in place, the subject targeted the same tidal volume (VT), respiratory rate, and inspiratory time fraction (TI/TTOT) recorded before NG tube placement. A computer program selected for analysis only those recorded breaths with and without an NG tube that were "matched" within 5 percent for both VT and TI. We calculated average VT, TI, and esophageal pressure fluctuation (delta Pes) for the matched breaths from each subject during every condition. The delta Pes values with and without NG tube were not statistically different in any tested condition (p > 0.05). Our data indicate that the presence of an NG tube does not invalidate the accuracy of delta Pes measurements made using a well-positioned balloon catheter in the tested conditions.