(Purpose) We developed an innovative transurethral resection system (TURis) consisting of a uniquely-designed generator and a resectscope. The obturator nerve is protected from trouble-some reflexes during TURis because the high frequency current delivery route is via the resection loop to the sheath of the resectscope and not via a patient plate. After extensive preclinical evaluation and verification of the system using an animal model to ensure efficacy as well as operational safety, TURis was conducted for treatment of superficial bladder cancer and benign prostatic hyperplasia.(Materials and Methods) In preclinical experiments swine bladder wall was transurethrally resected using the system in a saline environment. The results were compared with data obtained from an identical resection using the conventional system using sorbitol solution irrigation. Electrolytic contents were measured after TUR for comparative evaluation vis-a-vis corresponding pre-TUR data. Also, the depth of heat degeneration was measured in the resected tissue. From December, 2000 to June, 2002, TURis was performed in 25 cases of superficial bladder cancer and 30 cases of benign prostatic hyperplasia (BPH), using saline irrigation. All 55 cases were performed under spinal anesthesia without an obturator nerve block. The output power was set at 280W for cut and 120W for coagulation. A smaller electrode than those used in conventional TUR was used to improve the cutting efficacy. Occurrence of obturator nerve reflexes, difference of hematocrit and electrolytic contents before and after TURis, operation time and total volume of irrigated saline were evaluated.(Results) TURis in animal model: No adductor contraction of a lower limb was observable except for minimal creeping during the resection of a site close to the urethra. There were no apparent anomalies relative to the blood electrolyte content after TURis. No difference was observed in the mean depth of heat-degeneration tissue change compared with the conventional system. TURis for bladder cancer and BPH: No additional skills were required for TURis compared to conventional TUR. No obturator nerve reflex was observed except for a clinically insignificant thigh movement in one case of bladder cancer. The post-TURis blood tests manifested no significant anomalies in blood electrolyte content. Mean operation time for bladder cancer and BPH were 32 and 42 minutes respectively. Mean volumes of saline consumed during TURis were 6, 083ml for bladder cancer and 16, 100ml for BPH.(Conclusions) TURis worked effectively in a saline-irrigated environment. It does not need a patient plate and obturator nerve block even in cases of bladder cancer on the lateral wall. In addition, saline was both safe and cost-effective compared to non-electrolytic solution as irrigant for TUR of BPH. This suggests that TURis may have more applications than conventional TUR.