In recent years interest has increased in the biological effects and possible health outcomes of weak electric and magnetic fields. Studies have been presented on magnetic fields and cancer, reproduction, and neurobehavioral reactions. Epidemiologic studies on childhood leukemia and residential exposure from power lines seem to indicate a slight increase in risk, and excess leukemia and brain tumor risks have been reported in "electrical" occupations. In spite of a large number of experimental laboratory studies, however, no plausible and understandable mechanism has been presented by which a carcinogenic effect could be explained. International guidelines state that the scientific knowledge on magnetic fields and cancer does not warrant limiting exposure levels for the general public and work force down to the low levels of everyday exposure. Study results on reproduction, including adverse pregnancy outcomes, and neurobehavioral disorders are generally considered insufficiently clear and consistent to constitute a scientific basis for restricting exposure.