Octreotide is increasingly being used in the treatment of acromegaly. It effectively suppresses growth hormone secretion but also has inhibitory effects on gastrointestinal regulatory peptides and induces gallbladder paresis, which may predispose to gallstone formation. In nine acromegalic patients receiving long-term octreotide treatment gallbladder emptying, assessed by 99Tc-EHIDA scintigraphy after a standard fatty meal, was significantly impaired (p less than 0.005) when compared with normal healthy control subjects. Asymptomatic gallstone formation occurred in one patient who had the most severely impaired gallbladder emptying. Between 24 and 96 h after cessation of octreotide, in six of seven patients studied, gallbladder emptying had not only recovered but demonstrated significant rebound hypermotility (p less than 0.005). This finding has important implications for the administration of long-term octreotide therapy and suggests that a drug-free period each week may enable evacuation of gallbladder contents and reduce the risk of gallstone formation.