The effect of bolus viscosity on oropharyngeal and esophageal emptying is not known. We investigated this question in 38 healthy volunteers by measuring the transit of five semisolid boluses of varying viscosities across the oropharynx and the esophagus with the aid of scintigraphy. The studies were performed twice on consecutive days. The results show that oropharyngeal and esophageal emptying are reliably reproduced from day to day. Esophageal emptying was inversely related to bolus viscosity; however, oropharyngeal emptying was not influenced by bolus viscosity. We conclude that bolus viscosity has significant, but selective, effect on oropharyngoesophageal emptying.