The patch-clamp techniques are applied to the outer membrane of the nuclear envelope isolated from rat pancreatic acinar cells. The nucleus identified under an inverted microscope was removed by cell surgery from enzymatically dispersed single cells. All the patch-clamp techniques, in situ, excised, and whole-material recordings were applied to the envelope. We have found voltage- and Ca2+-activated K+-channels with an unitary conductance of 200 pS in the outer membrane. The channels are activated by lumen positive potentials and by an increase in luminal Ca2+ concentration. They may play a role for controlling Ca2+-release from the lumen of the nuclear envelope (endoplasmic reticulum) to the nucleoplasm and the perinuclear cytoplasm.