This testimony concerned NIOSH activities in the field of physical properties and biological effects of radiofrequency (RF) radiation from heaters and sealers. RF sealers and heaters have been used to heat, melt, or cure materials such as plastic, rubber or glue. NIOSH concluded from three preliminary industrial surveys in this area that the operators of this type of equipment were predominantly young women, that there was little if any awareness by the workers of the possible radiation hazard attendant with the operation of this equipment, and that the commercial equipment had not been developed to permit measurement of the radiation exposures to the employees. Studies conducted in 1974 to 1975 indicated that the majority of workers were exposed to RF radiation at levels up to ten times the ANSI standard of 10 milliwatts/square centimeter. Teratogenic studies indicated that high intensity RF produced fetal malformations when there were significant elevations in body temperatures. Specific biological effects of RF radiation were summarized including fatigue, irritability, cardiac and circulatory disorders, muscular weakness, electrocardiogram changes, headaches, insomnia, hypertension, changes in blood chemistry, nervousness, endocrine changes, changes in blood counts, electroencephalogram disturbances, decreased spermatogenesis, and a greater percentage of mongoloid children born to exposed fathers. Possible reproductive disturbances have also been noted along with chromosomal changes.