Female CD-1 mice were injected with an LD50 dose of Streptococcus pneumoniae and then exposed to 2.45 GHz (CW) microwave radiation at an incident power density of 10 mW/cm2 (SAR approximately equals 6.8 W/kg), 4 h/d for 5 d at ambient temperatures of 19, 22, 25, 28, 31, 34, 37 and 40 degs. C. The results showed that survival of sham exposed animals increased as ambient temperature increased until 37 degs. C when the thermoregulatory capacity of the animals was exceeded and deaths due to hyperthermia occurred. Survival of microwave exposed animals was significantly greater than the shams (approximately 20 percent) at each ambient temperature below 34 degs. C. An analysis of the data suggests that the hyperthermia from microwaves may be more effective in increasing survival than conventional hyperthermia. The results indicate that microwave radiation may be beneficial to infected animals at low and moderate ambient temperatures, but detrimental when combined with high ambient temperatures.