Administration of gallium nitrate to rats resulted in the formation of renal precipitates which occluded tubular lumina. When analyzed with a combination of scanning electron microscopy and x-ray energy spectrometry, these precipitates were found to contain gallium complexed with calcium and phosphate. Injection of gallium nitrate also resulted in hypercalciuria, although serum calcium levels remained unaltered. Administration of an osmotic diuretic, isosorbide, prior to gallium treatment resulted in the formation of fewer renal precipitates and histopathologic changes than in the nondiuresed animals. Diuresis did not alter gallium serum pharmacokinetics, the 24 hour cumulative renal excretion of gallium or the extent of the drug-induced hypercalciuria. However, isosorbide pretreatment significantly reduced the urinary concentrations of both gallium and calcium. The data presented indicate that diuresis reduces the severity of gallium-induced renal lithiasis and subsequent renal accumulation of gallium by diluting the urinary concentration of gallium and calcium thereby lowering the incidence of interaction of these two elements within the kidney tubule.