The absorption of irrigating fluid was measured by the ethanol method every 10 minutes during the course of 700 transurethral prostatic resections. The total blood loss was also measured using a photometer method. We found that ethanol determination is a convenient method of monitoring irrigating fluid absorption in daily practice. Absorption in excess of 150 ml. was detected in 46% of the operations. The volume of irrigant absorbed increased with the weight of the removed prostatic tissue, operating time and blood loss. The uptake of fluid usually started midway through the operation. Once absorption had started, there was an 87% probability that it would continue through the next 10 minutes with the exception of the last 10 minutes of surgery, when there was a 67% probability. A sudden decrease in arterial pressure coincided with the onset of fluid absorption 3.7 times more often than expected by chance. The absorption was no different in the 114 patients with a cancerous histology, compared to those with benign prostatic hyperplasia.