[en] This report presents a biological rationale for a possible role of ELF (extremely low frequency electric and/or magnetic) fields in the etiology of leukemia. The hypothesis is based on three lines of evidence: ELF fields may increase calcium efflux from cells, the intracellular concentration of oxygen radicals may increase as a result of increased calcium efflux, and certain leukocytes may be at exaggerated risk of oxidative damage resulting from increased calcium efflux because they produce oxygen radicals to do their job. An increase in the concentration of oxygen radicals may increase mutation to DNA and thereby increase risk of transformation. 23 refs