Repeated bladder contractions were evoked during a six month period in three unanaesthetized female minipigs by using unipolar carbon fiber electrodes embedded in the bladder wall adjacent to the ureterovesical junction. In contrast to bipolar and direct bladder muscle stimulation unipolar electrodes at each ureterovesical junction evoked bladder pressure increase similar to those produced in previous investigations in dogs. Sacral nerve stimulation of S2 evoked bladder contraction at a minimal current. Microscopic examination revealed no cellular reactions to the carbon fibers but a subcutaneous reaction to the receivers was seen and was thought to be due to mechanical irritation. The clinical implication of the findings is discussed.