The effects of carbamazepine (CBZ) on action potentials and calcium currents in cultured rat sensory spinal ganglion cells were investigated. CBZ was found to reversibly suppress the calcium-dependent components of action potentials and to reduce the amplitude of the after-hyperpolarizations, while the rising phase and the peak amplitude were hardly changed. Furthermore, CBZ caused a marked reduction in the calcium currents, which in some cells was reversible. The present findings confirm that CBZ has calcium-antagonistic properties.