Significant hyponatraemia has been reported following transurethral prostatectomy (TURP) in 11-41% of cases. The majority of previous studies have been performed retrospectively. A prospective study was undertaken of 100 patients undergoing TURP. In all, a 24-Charr sheath with non-irrigating, resectoscope and 1.5% glycine as irrigant was used. Volume of irrigant used, weight of prostate and length of procedure were recorded. Serum electrolytes were measured at anaesthetic induction and immediately on transfer to the recovery room. In none of the 100 patients was there a statistically significant fall in serum sodium following resection. No clinical changes of transurethral resection (TUR) syndrome occurred. This study confirms that TUR syndrome and a significant fall in serum sodium can be virtually prevented in TURP and the use of an irrigating resectoscope or a trocar in the average case is not necessary.