Epidemiological studies have indicated a modestly increased risk for the development of acute myeloid leukaemia in children who live close to high-voltage power-lines. Recent evidence has suggested that a common property shared by a number of known and suspected tumour promoters is their ability to block the process of apoptosis. Therefore, one possible mechanistic explanation for the apparent leukaemogenic effect of weak, low-frequency magnetic fields, such as emitted by power-lines and electrical appliances, would be their expression of tumour-promoting activity by interfering with the regulation of apoptosis in multipotent haemopoietic progenitor cells. In order to test this hypothesis, we have employed the well-characterized multipotential haemopoietic progenitor cell line FDCP-mix(A4). These cells are non-leukaemic and undergo apoptosis when deprived of appropriate growth factors such as Interleukin-3. We have tested a series of different regimes of weak, low-frequency magnetic fields: nulled fields, Ca2+-ion cyclotron resonance conditions at 50 Hz, and vertical 50 Hz fields of 6 microT(RMS), 1 mT(RMS) and 2 mT(RMS), exposing the cells for 2 hours, 24 hours, 4 days or 7 days under various culture conditions. We have not seen any significant alteration in apoptosis induced by any of the exposure regimes tested. We therefore conclude that the regulation of viability and apoptosis in FDCP-mix(A4) cells is not disturbed by weak magnetic fields of the magnitude and type indicated.