The teratogenic potential of microwaves was examined in a rodent species, the Syrian hamster. Exposure of hamsters to 2450-MHz CW microwaves at a power density of 20 mW/cm2 (estimated SAR = 6 mW/g) for 100 minutes daily on days 6-14 of gestation caused no significant change in fetal survival, body weight, skeletal maturity, or incidence of terata. Thirty mW/cm2 (estimated SAR = 9 mW/g) caused significantly increased fetal resorptions, decreased fetal body weight, and decreased skeletal maturity. Rectal temperatures of pregnant hamsters after exposure to 20 mW/cm2 were slightly increased (0.4 degrees C) over those of sham-irradiated dams; 30 mW/cm2 caused maternal rectal temperatures to be increased 1.6 degrees C over sham-irradiated dams' temperatures. It appears that the hamster fetus may be more susceptible to microwave radiation than the mouse.