Abstract.To establish the sensitivity of the gallbladder in relation to plasma concentrations of cholecystokinin, a dose‐response study was performed in five normal volunteers. Cholecystokinin octapeptide was infused in ascending incremental dose sequence, interval blood samples taken for estimation of plasma hormone concentrations and gallbladder emptying rates monitored continuously using99mTc‐HIDA. In five other volunteers, gallbladder emptying rates following a liquid fat meal were measured. Infusion rates of 0·0, 0·75 ± 0·2, 6·8 ± 0·5, 23·8 ± 1·6 and 66·1 ± 2·5 pmol cholecystokinin kg‐1h‐1produced plasma concentrations of<3·0 (undetectable),<3·0, 6·6 ± 1·8, 13·3 ± 1·5 and 26·9 ± 2·9 pmol l‐1respectively and gallbladder emptying rates (% min‐1) of 0·0, 0·0, 0·14 ± 0·15, 1·57 ± 0·38 and 4·29 ± 1·12. Following the fat meal, peak plasma cholecystokinin concentrations reach 30 pmol l‐1and gallbladder emptying rates (% min‐1) are 3·86 ± 1·01.We conclude that the threshold of the gallbladder to circulating cholecystokinin octapeptide is around 6 pmol l‐1, but that infusions which result in plasma levels of around 25 pmol l‐1produce gallbladder emptying rates comparable with those seen after oral fat. This suggests that the gallbladder is equally sensitive to endogenous and exogenous cholecystokinin and that plasma concentrations observed after o