Bile acid profiles in serum, urine and bile of Nagase analbuminemia rats (NAR) and Sprague-Dawley rats (SDR) were examined. Serum bile acid levels in NAR (2.02 + 0.51μg/ml, n=15, M ± S.E.) were markedly decreased as compared with those in SDR (20.86 ± 3.72 μg/ml, n=10). The unbound fraction of bile acids in serum examined by equilibrium dialysis was about ten times higher in NAR than in SDR. In the profiles of urinary and biliary bile acids in NAR and SDR, as big differences as seen for serum bile acids were not observed. Low bile acid levels in serum of NAR may reflect low bile acid binding capacity of NAR serum because the absence of albumin was thought to be one of the major causes of low bile acid levels in serum of NAR.