Isosorbide (5 mg/kg; a single p.o.) significantly increases the urine volume of rats within 2 hours which lasts through the 8 hour experimental period. Isosorbide (5 mg/kg; a single p.o. 30 min prior to gallium injection) significantly reduces the urinary concentrations of both gallium and calcium in rats. Isosorbide (5 mg/kg; p.o. 30 min prior to gallium injection for 6 d) results in the formation of fewer renal precipitates and histopathologic changes than in the nondiuresed animals.