A prospective study of the value of preoperative oesophageal manometry in selecting patients for gastro-oesophageal reflux surgery has been performed. One hundred and twenty-six consecutive patients had a floppy Nissen fundoplication with a median follow-up period of 48 months (range 21-96 months). Reflux was controlled in 116 patients (92.1 per cent). One hundred and five patients (83.3 per cent) had a clinically satisfactory result (Visick grades 1 and 2). Poor results were largely due to recurrent reflux, technical failure or the irritable bowel syndrome. An unsatisfactory result was not more likely in those with upright reflux, an oesophageal motility disorder or a competent cardia as defined by manometry. Preoperative oesophageal studies, other than those required to make an accurate diagnosis, were found to have no value in deciding the suitability of patients for surgical correction of gastro-oesophageal reflux.