The absorption of irrigation solution during transurethral prostatic resection may lead to the life-threatening condition of the so-called TUR syndrome. For a long time no early recognition procedure was easily and routinely available. This study was set up to investigate the effectiveness of ethanol as an early indicator of beginning absorption, as described by Hulten. Ethanol was therefore added to the irrigating fluid as a marker, and alcohol concentrations were measured in the exhaled breath. METHODS. For measurement of alcohol an Alcotest monitor 7110, Drägerwerk (Lübeck, FRG) was used. In preliminary experiments with 13 healthy volunteers the lowest amount of measurable i.v.-administered 2% Ringer-ethanol solution was found to be about 200 ml. The irrigating fluid used was a 2% ethanol-mannitol/sorbitol solution. RESULTS. The control of breath and blood alcohol levels in 10 patients undergoing transurethral bladder surgery showed that there was no absorption of alcohol across the internal bladder lining. Of 52 patients, who had to undergo transurethral prostatic resection, 23 had positive breath alcohol values of up to 0.81/1000. In 6 patients the blood alcohol levels only were elevated (max. 0.18/1000). In 23 other patients no increased blood or breath alcohol levels were detectable. The negative breath alcohol levels in 6 patients were most probably attributable to low breath volumes due to lack of cooperation caused by pre- and/or intraoperative sedation. There were no significant changes in central venous pressure, mean arterial pressure or heart rate even at the time of maximal alcohol levels, compared with initial values. These parameters thus cannot be used for the early recognition of beginning absorption. Simultaneous monitoring of serum sodium concentrations revealed significant decreases at the time of maximal breath alcohol levels. Yet, the first indication of beginning absorption was always a positive alcohol level. Serum sodium changes followed later with increasing alcohol levels. Sodium concentration did not drop before a positive alcohol level was measured in any of these cases. CONCLUSION. It was thus proven that the addition of ethanol to the irrigating fluid and monitoring of the patient's exhaled breath with the Alco-testmonitor is a simple, non-invasive system that can be routinely used for early detection of absorption during transurethral prostatic resection. Adequate adjustment of the further course of the operation was possible. The dreaded TUR syndrome did not develop in any of the patients monitored in this way.