We studied the combined effects of exposure to magnetic field (MF) 50 Hz 10 mT and X-ray ionizing radiation on developing chick embryos. When chick embryos at early stages were repeatedly exposed to MF prior to X-ray radiation, reduction of X-ray teratogenicity was observed. When MF exposures started immediately after X-ray radiation, the adverse developmental effects of ionizing radiation were potentiated. Embryotoxicity was more pronounced in X-ray irradiated and MF exposed groups. We present a hypothesis about the mechanisms of MF effect based on enhancement of oxidative processes, followed by stimulation of antioxidant systems.