High levels of applied laser irradiation to the prostate will carbonize or vaporize tissue, and may cause explosive expansion of superheated tissue water. Lower levels, used most often to relieve obstruction caused by benign prostatic hypertrophy, will cause coagulation necrosis. This effect is apparent within 1 h of application. In contrast to the canine, in which laser-coagulated prostate sloughs in 2 to 3 weeks leaving a smooth cavity, in the human necrotic tissue is sloughed irregularly over a period ranging up to 12 weeks. This difference is attributed to the dominantly glandular nature of the canine prostate, and the dense fibromuscular composition of the human prostate stroma. Sloughing is accomplished by surface liquefaction, cavitation of the necrotic coagulum, and to a lesser degree, formation of granulation tissue at the margins. As often occurs at the margin of spontaneous infarcts in the prostate, squamous metaplasia may be prominent at the margins of laser-induced coagulation necrosis.