The changes in serum electrolytes (sodium, potassium, ionized calcium, and total calcium) produced by high-dose (3 ml/kg) intravenous contrast media were investigated in Japanese white rabbits. The test solutions included sodium/meglumine diatrizoate (370 mgI/ml), sodium/meglumine ioxaglate (320 mgI/ml), iohexol (350 mgI/ml), iopamidol (370 mgI/ml), 20% mannitol, and isotonic saline. The alterations in serum ionized calcium were relatively small and transient, and correlated with changes in the hematocrit. Diatrizoate caused a significant decrease in ionized calcium in comparison with other contrast media and mannitol. The ratio of ionized calcium to total calcium showed no significant decrease in any group. The changes in potassium did not correlate with those in hematocrit. Diatrizoate caused a smaller decrease in potassium than low-osmolality contrast media, which may suggest that diatrizoate caused a shift in potassium from extravascular space to intravascular space. In conclusion, intravenous infusion of high doses of low-osmolality contrast media did not cause clinically significant alterations in serum electrolytes.