The effect of electroconvulsive shock (ECS) on the responsiveness to pain (measured by the hot-plate test) and on the characteristics of L-type calcium channels (measured as [3H]nitrendipine binding sites) in the cortex and hippocampus was tested on the Wistar rat. In animals receiving a single ECS, the calcium channel density and affinity 24 h after treatment did not differ from the controls; the response to pain was also at the control level. Repeated ECS (eight once-daily shocks) resulted in an increased responsiveness to pain (shortening of response latency) and in an increase in the density of cortical, but not hippocampal, calcium channels. The KD value for [3H]nitrendipine binding sites in either brain region remained unaltered by ECS. The calcium channel antagonist nifedipine, which by itself did not significantly alter the response to pain, prevented the enhancement of pain sensitivity brought about by ECS. The results suggest activation of calcium-dependent mechanisms by repeated ECS and confirm the involvement of calcium channels in pain mechanisms.