Bile composition and secretion were studied in tow elasmobranch species, Squalus acanthias (spiny dogfish shark) and Raja erinacea (small skate), after ligation of the common duct and insertion of cannulas into the gallbladder lumen. Fish were then allowed to swim freely in large pools and bile was collected in balloons attached to the externalized cannulas. Both species secreted bile for periods of 4-7 days at a maximum rate of 1.77 +/- .89 ml/kg per 24 h in Squalus acanthias and 2.66 +/- .89 ml/kg per 24 h in Raja erinacea. Comparison of the composition of cannula and gallbladder bile indicated that hepatic bile could be collected by this technique in both species without effective contact with gallbladder epithelium. The low concentrations of HCO3- and CL- and the gigh bile salt levels in dogfish gallbladder bile indicate that mechanisms for concentration and acidification of bile in the gallbladder developed early in vertebrate evolution. These results indicate that gallbladder cannulation in free-swimming elasmobranchs is a useful technique for the study of bile secretory and excretory function in marine species.