To evaluate the usefulness of the volumetric fluid balance for indicating and quantifying fluid absorption during transurethral resection of the prostate, 62 patients showing fluid absorption on ethanol monitoring (control method) were selected from a series of 410 operations. The volumetric fluid balance, which was measured as the difference between the input and output of irrigating fluid with and without a correction for the blood loss, proved to be an unreliable clinical tool for measuring the absorption. It indicated that fluid absorption occurred only in 40 or 18 of the 62 patients, depending on whether a correction for blood loss was made or not, the volume being only 59% and 71% (median), respectively, of that obtained by the control method. The absorption averaged 1 L in the patients in whom the volumetric measurements did not indicate absorption. The incidence of symptoms of the ‘transurethral resection syndrome’ increased with the absorbed fluid volume only when measured by the control method.