Several studies have been undertaken to elucidate the effects of electromagnetic field (EMF) on intracellular calcium ([Ca2+](i)) in the past 20 years. However, still there were controversies of electromagnetic pollution within the scientific community. In this work, we studied the effects of alternative magnetic fields on intracellular calcium. Osteoblastic cells were used as a model both to test the hypothesis that extremely low-frequency (ELF) magnetic fields can alter the concentrations of the intracellular calcium, and to examine the 'window' effect predicted by our previous theoretical work. The outcome of this experiment demonstrated that 50 Hz, 0.8 mT magnetic field can induce the uptake of [Ca2+](i) in osteoblasts. The empirical evidences of the specified window effects of [Ca2+](i) in osteoblastic cells were reported for the first time in this work. (C) 2010 Elsevier Inc. All rights reserved.