Summary We examined the value of impedance monitoring in measuring bolus volume compared with videoesophagram. Eighty consecutive subjects were studied with simultaneous impedance-manometry-videoesophagram. A catheter with both an impedance electrode pair and a pressure transducer at four sites (5, 10, 15, 20 cm above lower esophageal sphincter) was passed per nares. Six 10-cc boluses of 45% barium mixed with 0.9% NaCl were swallowed at 20-to 30-second intervals. When impedance fell to below