Data which purport to show that patients undergoing prostate surgery can be protected from excessive bloodloss through the prior administration of an estrogen are presented. Some assumptions that must be made in order to assure that a test of measured bloodloss is equivalent with a test of the actual bloodless these quantities differing by a random error were pointed out. It was concluded that the use of an estrogen is effective in reducing bloodloss at the 5 per cent significance level, but this is insufficient evidence to conclude that it reduces the length of time necessary for the operation. The treatment does seem to reduce the weight of the tissue removed at the 20 per cent significance level. (Author).