Background: Epidemiologic data revealed increased brain tumor incidence in workers exposed to magnetic fields (MFs), raising concerns about the possible link between MF exposure and cancer. However, MFs seem to be neither mutagenic nor tumorigenic. The mechanism of their tumorigenic effect has not been elucidated. Methods: To evaluate the interference of MFs with physical (heat shock, HS) and chemical (etoposide, VP16) induced apoptoses, respectively, we exposed a human glioblastoma primary culture to 6 mT static MF. We investigated cytosolic Ca 2ϩ ([Ca 2ϩ ] i ) fluxes and extent of apoptosis as key endpoints. The effect of MFs on HS-and VP16-induced apoptoses in primary glioblastoma cultures from four patients was also tested. Results: Static MFs increased the [Ca 2ϩ ] i from a basal value of 124 Ϯ 4 nM to 233 Ϯ 43 nM (P Ͻ 0.05). MF exposure dramatically reduced the extent of HS-and