Visual Laser Ablation of the Prostate has been shown to be an effective treatment for the relief of bladder outlet obstruction secondary to benign prostatic hyperplasia. Dosimetry studies using the potato and live canine model are commonly used to advocate application of the Nd:YAG energy into the prostatic tissue. Questions have been raised as to the accuracy of tissue heat penetration in such models based on the scatter and diffusion caused by variations in blood flow and tissue differences from one prostate to another. Thus a study was done to evaluate differences, it any, in heat energy penetration caused by blood flow in the prostate. Mature canine prostates were lased in the (1) live dog, (2) euthanized dog, and (3) en bloc resected canine prostates immersed in a water bath of 101 degree(s)F. Prostates were lased using 60 watts for 60 seconds in the 2, 4, 8, and 10 o'clock positions. One prostate model was lased in the 8 and 10 o'clock positions while alive and then removed in bloc, immersed in a water bath at 101 degree(s)F and lased at the 2 and 4 o'clock positions. A third prostate, having been completely removed two days prior to lasing and frozen, was immersed in a water bath at 101 degree(s)F and lased. The findings indicate in the resected prostate loss of the ring of thermal damage, however, a zone of coagulative necrosis which is consistent with that seen in the live model. Thus blood flow does not appear to have a significant effect on Nd:YAG depth of penetration.