Objective To determine the agreement between on-table weighing and the ethanol breath test in measuring the fluid absorption of patients during transurethral prostatectomy (TURP), and to assess the practicality of on- (14) g at a mean resection rate of 0.74 g/min. The mean (range) absorption using the balance was 456 ( -343 to 2486) mL, and using the ethanol breath test was 435 (44-2750) mL, with the mean of the differences being -17 mL, with a 95% confidence interval (CI) of -81 to -40, the 95% limits of agreement being -389 to 356 mL (95% CI -458 to -337 and 297 to 418 mL). Conclusions Both methods are comparable and measure irrigating fluid absorption to levels of accuracy that are useful clinically. Either method could (and should) be used in routine practice.