The present study was designed to test the hypothesis that the presence of a specific hepatobiliary disease, namely common bile duct obstruction, in the absence of other risk factors will exacerbate gentamicin nephrotoxicity. Furthermore, since bile duct ligation decreases urinary calcium excretion, we studied the role of calcium supplementation in the prevention of gentamicin nephrotoxicity in this model. Male Sprague-Dawley rats were allocated to sham groups and common bile duct ligation groups. Gentamicin at 40 and 100 mg per kg per day for 5 days induced a more severe azotemia in common bile duct ligation animals than in sham controls. Furthermore, higher levels of renal gentamicin were found in common bile duct ligation rats than in sham rats early in the course of therapy, at its termination and during the recovery period. Pretreatment of common bile duct ligation animals with dietary calcium supplementation significantly attenuated gentamicin nephrotoxicity and the increased renal gentamicin accumulation, whereas initiation of calcium supplementation concurrent with gentamicin administration had no salutary effect. We conclude that experimental extrahepatic cholestasis in the rat, in the absence of any other factor, potentiates gentamicin nephrotoxicity. The effect is prevented by pretreatment with dietary calcium supplementation but is not modified by concurrent administration of a high-calcium diet.