The influence of extremely low frequency electric magnetic fields. (ELF EMFs) on apoptotic cell death was examined using a human leukemic cell line, HL-60 and normal human peripheral blood leukocytes. When HL-60 cells were exposed to 45 mT ELF EMFs, apoptotic cell death, characterized by cell shrinkage, nuclear fragmentation and cleavage of internucleosomal DNA to yield fragments that were multiples of 180-200 base pairs, were induced. The minimum periods required apoptotic HL-60 cell death was 1.0 hour. However, exposure to ELF EMFs could not produce detectable DNA fragmentation in human peripheral blood leukocytes. Static magnetic fields could not induce apoptotic cell death in HL-60 cells, even when the cells were exposed to 180 mT of magnetism for 3.5 hours. We further examined whether hyperthermia induced by induction current in ELF EMFs produced apoptosis in HL-60 cells. Induction current in ELF EMFs enhanced temperature of culture medium to 40.3 degrees C at 3.0 hours of exposure. However, this level of temperature could not induced apoptotic cell death in HL-60 cells, even when cells were cultured for 3.5 hours. These results suggest that induction current produced by ELF EMFs may be one of main mediator in apoptosis in HL-60 cells.