The size and composition of the bile salt pool has been measured in patients with untreated coeliac disease and in control subjects. The total bile salt pool was markedly increased in coeliac patients, the average being 9.2 grams compared with 3.1 grams in controls. Taurocholate synthesis was normal, consistent with its enlarged pool and prolonged half-life. Half-life and pool size were significantly correlated. The composition of the bile salt pool was virtually identical in the two groups. Our findings suggest that as the enterohepatic circulation is slowed by gallbladder inertia, so hepatic surveillance of pool size is diminished.