To quantitate electrosurgical and tissue variables during transurethral prostatic resection and electrovaporization, these procedures were performed in five patients using standard endoscopic equipment and the Erbe ICC 350 electrosurgical generator. Current, voltage, power, and resistance were monitored continuously. Energy transfer was quantitated during each electrode pass. Prostatic resection or electrovaporization was successful in each patient. Current, voltage, resistance, and power were similar during resection and electrovaporization, whereas energy transfer was greater during electrovaporization. Generator and tissue characteristics can now be precisely monitored and instantaneously altered during transurethral prostatic electrosurgery to minimize energy transfer to the patient while producing the desired tissue effects.