Rats were exposed to a hyperthermal environment or 1600 MHz radiation for 10 minutes to achieve equivalent rectal temperature increase (4 degrees C). Brain areas were quantitatively assayed for changes in magnesium, calcium, copper, zinc, iron, sodium, and potassium. Iron was increased in several brain regions of both hyperthermal and irradiated animals. Copper content of the cortex was also increased in both experimental groups, whereas zinc was decreased in the hypothalamus. Magnesium was increased in the cortex and medulla of the irradiated rats.