Esophageal acid clearing in normal subjects was studied in different body positions, with an assessment of reproducibility, after dry and water swallows, after smoking, and after alcohol intake. A significant increase in the number of swallows to raise the distal esophageal pH to 5.0 was found in the head-down position (p less than 0.003), after smoking (p less than 0.003), and after alcohol intake (p less than 0.001). It is proposed that the outcome of the acid-clearing test reflects both the transporting capacity of the esophageal muscles and the production of saliva. The precision of the acid-clearing test is not satisfactory, which makes it unsuitable for use in individual cases. It seems, however, well fitted for evaluation of esophageal acid clearing in larger samples.