Voltage-activated calcium channel function was examined in cultured GH3 cells using the whole-cell patch clamp technique. Exposure to a 120 mT static magnetic field resulted in a slight reduction in the peak calcium current amplitude and shift in the current-voltage relationship. The most significant change was a slowing of the channel activation rate without any change in the inactivation rate. All changes in channel function were reversible, with return to pre-exposure values within 3 min after the field was turned off. These alterations in channel function were temperature-dependent. The present findings are consistent with a functional disruption of the intramembranous portion of the calcium channel by a magnetically induced membrane deformation.