Over a 6-year period 264 cholecystokinin (CCK) provocation tests have been performed in 174 patients with undiagnosed right upper quadrant pain. All were carried out by one person (T.W.J.L.) as part of a prospective placebo-controlled crossover study. Following infusion of CCK but not saline, 103 patients developed pain (CCK + ve). These patients were offered cholecystectomy and 90 accepted. Seventy patients developed no pain during either infusion (CCK - ve), and one patient experienced pain with both CCK and saline infusions. Of the 90 patients who underwent cholecystectomy, 81 (90 per cent) have been followed up for a mean of 35 months (range 12 months to 5 1/2 years), 67 per cent have had complete resolution of symptoms and a further 24 per cent have had a marked improvement in symptoms. Only 9 per cent of patients did not benefit from cholecystectomy. This compares well with patients undergoing cholecystectomy for uncomplicated calculous gallbladder disease, 88 per cent of whom, in our study, were improved by surgery. Patients with a positive CCK test have an excellent chance of symptomatic improvement following cholecystectomy.