Current evidence suggests that lower oesophageal sphincter (LOS) competence depends upon both pressure and length. Existing devices can measure length and pressure, but not simultaneously. This methodological problem is a fundamental drawback to understanding LOS function and its role in oesophageal disease. A 'sphinctometer' has been developed, consisting of an oil-filled 3-mm diameter Silastic chamber, 6 cm in length, incorporating a pressure microtransducer designed to provide an integrated pressure reading as a function of length. Its performance has been tested in vitro using human cadaver oesophagus in a specially constructed chamber in which sphincter length and pressure can be varied independently. Comparisons were made with a conventional pull-through technique. Sphinctometer response was linear throughout the LOS pressure range of 0 to 50 mmHg at a fixed LOS length (RS = 0.99; P less than 0.001). Sphinctometer response was also linear at fixed LOS pressure for sphincter lengths from 1 to 6 cm (RS = 0.99; P less than 0.001). This device thus appeared suitable for monitoring function of the human LOS, and has subsequently been successfully incorporated into an ambulatory system for patient use.