Several different methods have been applied to measure the extent of bile salt deconjugation (deamidation), if any, outside the gastro-intestinal tract of the rat. A breath test has been applied to the rat using peroral or intravenous administration of cholyl-glycine-1-14C. Results for normal rats have been compared with rats with a continuous recirculation of bile to a tail vein. Bile salts labelled with 2,4-3H in the sterol moiety and conjugated with glycine-1-14C have been infused in rats and recirculated via a bile duct tail-vein shunt. The 3H:14C ratio in the bile has been used as an indication of deconjugation. In these experiments the radioactivity pattern of the bile salts has been determined after thin-layer chromatography. Different labelled bile salts have also been infused intraperitoneally and the composition of bile secreted through bile fistulae studied. In none of these experiments, in which the gastro-intestinal content was bypassed and a return of bile salts to the liver in the physiological range ensured, was any deconjugation of glycine-conjugated bile salts observed. When the liver, however, was stressed by anaesthesia and the intraportal infusion of deoxycholyl-2,4-3H-glycine in unphysiological levels, deconjugation occurred as indicated by the appearance in bile of labelled taurine conjugates. In these rats the dose of deoxycholylglycine was clearly toxic as evidenced by partial or complete cholestasis and eventually death of the animal.