Laser Doppler perfusion monitors are effect tools in understanding blood flow in many different types of biological studies. Because the low-intensity lasers used in Doppler perfusion measurements must interact with moving blood cells, the depth of probe-able tissue is limited to the volume of tissue within the hemisphere of radius ~1mm from the probe tip. In addition, heterogeneities in surface perfusion make precise probe placement very important if one is comparing successive measurements. Consequently, useful tissue perfusion measurements have been difficult to obtain, especially in deep tissues. In this study, a new method was developed for monitoring deep-tissue blood perfusion directionally with the Laserflo laser Doppler perfusion probe. The probe was inserted just under the skin superficially to a rat prostatic tumor through the shaft of a 16-gauge needle, which was modified to allow the probe to be exposed without extending beyond the beveled needle tip. Perfusion measurements of the tumor surface or the skin were made by rotating the bevel to face either inside or outside. Using this technique, tumor tissue can be differentiated from either skin or muscle. To study the responses of tumor to light stimulation, an 805nm biomedical treatment laser was used to irradiate the tumor. The perfusion of the tumor surface was shown to decrease slightly with short treatment laser applications (1W for 30 seconds or 1 minute). After a longer treatment session (5 minutes), the perfusion of the tumor tissue increased significantly. However, with an even longer (10 minutes) treatment, the perfusion of the tumor surface was shown to decrease once again. This trend indicates that before laser heating becomes significant, the perfusion decreases for as yet poorly understood reasons. When laser heating becomes significant, after the five-minute session, the perfusion increases dramatically, corresponding to the expected dilation of blood vessels during tissue heating. After further treatment, we observe decreased perfusion again corresponding to the point, at which tissue temperatures increase to tissue- and blood vessel- damaging levels, causing a decrease in perfusion.