We have examined the possibility of assessing primary bile acid pool sizes from the spillover of the bile acids into systemic blood after intestinal exposure to the total endogenous bile acid pool; the studies were carried out in 16 healthy subjects. Bile acid spillover was calculated as the integrated area under the curve of bile acid conjugates in serum of each primary bile acid class in response to a well-defined sustained cholecystokinin-induced stimulus of the enterohepatic circulation for 55 min causing complete gallbladder emptying. Serum levels of each species of primary bile acid conjugates were measured by two specific and sensitive radioimmunoassays, one for conjugated cholate and one for conjugated chenodeoxycholate. Primary bile acid pool sizes determined with [24-14C]cholic acid and [24-14C]chenodeoxycholic acid according to Lindstedt (1957. Acta Physiol. Scand. 40:1-9) served as reference. Bile acid conjugates of both species reached a peak 70 min after the start of the cholecystokinin infusion, probably reflecting simultaneous intestinal absorption of both primary bile acids in this model. Highly significant linear correlations were found between the integrated areas under the curve and primary bile acid pool sizes, which were closer for chenodeoxycholate (n = 16, r = 0.81, P less than 0.001) than for cholate (n = 16, r = 0.74, P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)