The quantitative and qualitative distribution of bile salts in the duodenal juice of 13 patients with cystic fibrosis (CF) was studied after a test meal. The effects of triolein (TO), bovine serum albumin (BSA), and ricinoleic acid (RA) on the absorption of taurocholate (TCA) in the distal ileum of the rat in vivo was also studied. The mean (and ranges) of total bile salt concentrations, glycine: taurine conjugate ratios, and percentage of dihydroxy bile salts in the patients with CF and pancreatic insufficiency were 3.5 (1.3--6.6) mmol/l, 8.6 (greater than 10-3.1), and 37 (10--60) compared with control values of 7.4 (3.0--16.0) mmol/l, 3.0 (1.3--4.5), and 61 (52--70) respectively. The differences between the control and CF values were statistically significant (P less than 0.01--P less than 0.001). Three of the 13 CF patients had total bile salt concentrations less than 2 mmol/l, 8 had much higher glycine: taurine ratios, and 8 had a reduced percentage of dihydroxy bile salts. In 2 patients with normal pancreatic enzyme activities, duodenal bile salts were both quantitatively and qualitatively normal. TO (10 and 30 mmol/l), BSA (3%), and RA (5 mmol/l) had no inhibitory effect on the ileal absorption of TCA. These results show pronounced abnormalities of duodenal juice bile salts in CF with pancreatic insufficiency consistent with a broken enterohepatic circulation (EHC); such abnormalities may contribute to defective lipid absorption in CF. The data in the experimental animal do not support the suggestion that unhydrolysed dietary substrates play a role in the pathophysiology of the broken EHC.