Possible regulation of trace metal metabolism by various steroid hormones has been reported by a number of investigators. The purpose of the present study was to determine the effect of aldosterone on the serum copper, zinc, and magnesium concentrations in the rat. Male and female rats were infused with aldosterone for up to 72 h and the serum copper, zinc, and magnesium concentrations were determined. The serum zinc concentration exhibited a transient decrease with a nadir at 24 h. No significant change was observed in serum magnesium or copper that was directly attributable to aldosterone. The mechanism by which aldosterone affects the transient serum zinc decrease was not demonstrated, but several possibilities were discussed.