The embryofetal toxicity and teratogenicity of plane-wave 2.45 GHz continuous wave (CW) microwave radiation at different intensities were investigated in the CD-1 mouse. Mice were exposed on days 1-15 of gestation to an incident power density of 5 mW/cm2 (specific absorption rate of 6.7 mW/gm) and either on days 1-6 or 6-15 of gestation to 21 mW/cm2 (specific absorption rate of 28.14 mW/gm) or to 30 mW/cm2 (specific absorption rate of 40.2 mW/gm) for 8 hours daily. Exposure either on days 1-6 or 6-15 of gestation to a power density of 21 or 30 mW/cm2 caused an increase in colonic temperature of exposed dams of 1 degree C and 2.3 degrees C, respectively. To distinguish between "thermal" and "nonthermal" effects of 21 or 30 mW/cm2, groups of mice were also exposed to elevated ambient temperature to raise their body temperature to the level of those animals exposed to microwave. Ambient temperatures of 30 degrees C and 31 degrees C increased the deep colonic temperature to that obtained with the 21 and 30 mW/cm2 microwave exposure, respectively. The temperature-exposed mice were handled in exactly the same manner as the microwave-exposed mice. A significant reduction in maternal weight gain, either during treatment on days 1-6 or 6-15 of gestation was observed in females of all handled groups. Handling plus exposure to elevated ambient temperature (30 degrees C or 31 degrees C) during days 6-15 of gestation increased this reduction in maternal weight gain. A significant decrease in implantation sites per litter and reduction in fetal weight was noted in the group exposed to 30 mW/cm2 during days 1-6 of gestation. Exposure of mice to a power density of 30 mW/cm2 (days 6-15 of gestation) resulted in a slight, but significant increase in the percentage of malformed fetuses, predominantly with cleft palate, when compared to all other groups.