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Behavioral and thermal effects of radiating an animal with differing wavelengths of microwave energy at the same power density were investigated in the first of two studies. Five Long‐Evans rats were trained to perform a lever‐pressing task and were rewarded with food on a variable interval schedule of reinforcement. Rats were individually exposed in random order to 400‐, 500‐, 600‐, and 700‐MHz CW radiation at a power density of 20 mW/cm2 with the long axis of the rat's body parallel to the vector of the electric field. Radiation at all wavelengths produced rises of body temperature and stoppage of lever pressing. The averaged rise in body temperature was greatest and work stoppage was most rapid during exposures at 600 MHz. In the second study, six rats were exposed in random order to 600‐MHz CW radiation at power densities of 5, 7.5, 10, and 20 mW/cm2 while performing the same behavioral task. Exposures at 10 and 20 mW/cm2 resulted in work stoppage, while exposures at 5 and 7.5 mW/cm2 did not. In addition, three of the rats were subsequently exposed while responding to 600‐MHz pulsed radiation (1000 pps, 3‐ or 30‐μs pulse durations at a peak power density of 170 mW/cm2 (averaged 0.51 and 5.1 mWcm2). No work stoppage occurred to pulsed radiation. Taken in sum, the data show that the mature Long‐Evans rat is resonant at a frequency near 600 MHz while work stoppage during short‐term exposures to 600‐MHz radiation occurs at a power density between 7.5 and 10 mW/cm2.

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Long-Evans male adult rats were exposed for sixteen weeks to 2450-MHz CW microwaves at an average power density of mW/cm2. The resulting dose rate was 1.23 (+/- 0.25SEM) mW/g. The animals were exposed eight hours a day, five days a week, for a total of 640 h in a monopole-above-ground radiation chamber while housed in Plexiglas holding cages. Daily measures of body mass and of food and water intakes indicated no statistically significant effects of microwave irradiation. Biweekly stabilimetric tests immediately after exposure revealed a significant depression of behavioral activity by 15 microwave-exposed rats as compared with 15 sham-exposed animals. Measures of locomotor activity based on revolutions of a running wheel, which were obtained during 12-h periods between each 8-h exposure, showed no significant effect of irradiation. Blood sampled after 2, 6, 10, and 14 weeks of exposure indicated slight alterations of sulfhydryl groups, and of red and white blood-cell counts. Measures of levels of 17-ketosteroids in urine at weeks 1, 5, 9, and 12 of exposure, and mass of adrenals, heart, and liver at the end of the sixteen-week period of exposure, revealed no indications of stress.