Recently, a mutant rat strain was described with a genetic defect for the biliary excretion of organic anions (TR-rats). To determine the possible heterogeneity of the transport systems in liver, intestine and kidney we investigated the transport of the anion 1-naphthol-beta-D-glucuronide (1-NG) in isolated vascularly perfused organ preparations of the rat liver, intestine and kidney of both Wistar rats and TR- rats. 1-NG was administered as such (liver and kidney experiments) or formed intracellularly from 1-naphthol (1-N) (liver and gut experiments). Independent of the type of exposure to 1-NG, the biliary excretion was considerably impaired in TR- rats. In the intestine the total appearance and the vascular/luminal distribution pattern of 1-NG were not significantly different from the values in control rats. Furthermore, no significant disturbance was found with respect to the renal clearance of 1-NG in the TR- rat when compared with the Wistar rat. Thus, the genetic defect in the TR- rat is restricted to an impaired hepatobiliary excretion of 1-NG and does not affect the excretory systems of the intestine and kidney. These results suggest that the excretion of 1-NG by the liver, intestine and kidney involves distinct organ-specific transport systems.