Two systems for exposing mice to 2,450-MHz electromagnetic fields are described. In a waveguide system, four mice were placed in a Styrofoam cage and exposed dorsally to circularly polarized electromagnetic fields. The temperature and humidity in the mouse holder were kept constant by forced-air ventilation. For 1-W input power to the waveguide, the average specific absorption rate (SAR) was determined by twin-well calorimetry to be 3.60 plus or minus 0.11 (SE) W/kg in 27-g mice. The maximum SAR at the skin surface determined thermographically was 8.36 W/kg in the head of the mouse. The second system was a miniature anechoic chamber. Six mice were irradiated dorsally to far field plane waves. Copper shielding and high-temperature absorbing material were lined inside the chamber to accommodate the high input power.