We systematically determine the depth of coagulation necrosis induced during Nd: YAG laser irradiation in the prostate of 17 mongrel canines, to define the correlation of laser dose with depth of the lesions. The laser radiation was delivered via a UrolaselN catheter. The effect of various dosimetries on prostatic tissue were investigated using laser power in the range of 8 to 60 watts (W) at varying exposure times, from 20 to 300 seconds (5) . Applied energy ranged from 1. , 000 to 5 , 500 Joules (J). Three distinct features were observed. First, deep coagulation necrosis was induced only with laser regimens of ≥2,100J, suggesting that there is a threshold of energy that must be overcome in order to achieve significant coagulation depth. Second, the deepest coagulation necrosis was achieved with a low power - slow heating regimen (15W X 1805). Tissue surface changes appeared to be responsible for the reduced depth of coagulation necrosis seen with higher power regimens (Barbecue effect). Third, increasing the energy above 3,600J did not augment the depth of coagulation, suggesting that a steady state for temperature distribution is reached at approximately that rate of heating. Our study suggests that a low power - slow heating regimen of 15W X l8OS yields larger volumes of coagulation necrosis than other regimens.