The in vivo dehydration of the Acuvue disposable contact lens was measured in six subjects using a contact lens refractometer. On average, the lenses dehydrated 6.2 +/- 1.9% after 20 min and 10.2 +/- 3.9% after 6 h of wear. The magnitude of dehydration is greater than has been reported for other hydrogel lens types of similar water content. This information may assist practitioners in the interpretation of clinical signs pertaining to lens behavior and associated patient symptoms.