Power of oesophageal peristalsis can be controlled voluntarily. The hypothesis that oesophageal peristalsis can be modified voluntarily was explored. Six healthy male volunteers and eight female patients with angina like chest pain underwent oesophageal manometry. Each was asked to take a series of swallows, and to vary their size, in random order, by taking either a big gulp or a little swallow. None of the subjects experienced difficulty in doing so. In both groups the amplitude of oesophageal contractions were significantly greater after big gulps than little swallows (p less than 0.01) and this was true for wet (82.0 v 68.9 mmHg) and dry swallows (52.3 v 43.3 mmHg). For the patients' wet swallows the mean values were 73.0 and 56.0 mmHg. Thus, the amplitude of oesophageal peristalsis can be controlled voluntarily. This effect may account for some of the within subject variation in the amplitude of oesophageal contractions. During oesophageal manometry subjects should be encouraged to standardise the size of their swallows whenever possible. Patients with symptoms related to abnormal oesophageal peristalsis such as dysphagia, heartburn, and chest pain may benefit from biofeedback training. 