Since Wertheimer and Leeper reported in 1979 that children living near power distribution lines have as high as twice or three times the incidence of cancer, the relation of leukemia or cancer to extremely-low-frequency (ELF) electromagnetic field (EMF) has been a subject of repeated argument. We cannot sum up the bioeffects of EMF in a few words, for these are attributed to frequency difference. This review discusses the bioeffects of EMF ranging from frequency of microwave to static magnetic field with main stress on the socalled non-thermal effects below radiofrequency band. Non-thermal effects are rather weak compared with those of high frequency band and have been treated as unknown matter for a long period. However, as the EMF energy has come to be increasingly used at high levels, we can now clearly detect the bioeffects of induced eddy currents. On the other hand, some findings about low level ELF electromagnetic field suspected as a cancer-promoting factor are mainly gained by epidemiological method. Cancer researchers concerned with recent powerline issues are coming up with many reports on oncological effects of very low-level (0.1 microT order) ELF electromagnetic fields. More data, however, should be collected to reach appropriate conclusion about the possibility of low level ELF electromagnetic fields have an effect of cancer promotion. As for the safety standards of static magnetic field it should be noted that in 1993 National Radiation Protection Board (UK) and International Radiation Protection Association published the highest values ever recommended. These announcements would agree with our assumption that biological processes require high flux density of ELF-EMF proportional to 1/f, where frequency and flux density are indicated with a logarithmic function.