The teratogenicity and embryotoxicity of high intensity 27.12 megaHertz radiofrequency radiation was studied. Pregnant Sprague- Dawley-rats underwent separate whole body irradiation at a frequency of 27.12 megaHertz until a rectal temperature of 43.0 degrees-C had been reached, with specific absorption rates ranging from 11.1 to 12.5 milliWatts per gram. Pregnant controls were sham irradiated, with an untreated control group also being employed. All rats were sacrificed on gestation day 20. More than 200 different types of abnormalities were observed in irradiated fetuses. Numerous variations in skeletal development occurred in both irradiated and control fetuses. Colonic temperatures above 43.0 degrees were increasingly lethal, with no fetal malformations occurring below 41.9 degrees and with no rat surviving above 43.5 degrees as a result of hyperthermia. Gestation day 9 was most sensitive to radiofrequency teratogenesis, with craniofacial malformations predominating. The authors conclude that 27.12 megaHertz radiofrequency radiation sufficiently intense to cause appreciable body heating is definitely teratogenic in rats, and that the extent and severity of the malformations produced depend upon intensity and duration of exposure. It is further concluded that the majority of the malformations observed, which included anophthalmia, microphthalmia, exencephaly, cleft palate, micromelia, syndactyly, ectrodactyly, hydrocephaly, short digits, and short or absent tails, probably resulted from direct embryo damage incurred during exposure. The authors recommend that radiofrequency radiation, if sufficiently intense to cause body tissue heating, should be considered a potential hazard to the human embryo, and that more research should be conducted in order to determine whether or not workers exposed to such radiation exhibit adverse reproductive effects.