The contractor has proposed to develop a NdYag (Neodymium- Yitrium-Aluminum-Garnet) laser based system for interstitial and external beam hyperthermia for the treatment of cancer. It would provide local hyperthermic heating which would not have constructive/destructive interference problems and which can be monitored and controlled by the use of an inexpensive microthermal couple system. Phase-I studies will include (1) determination of the optimum NdYag wavelength to be used (1.06 or 1.32 microns), (2) what is the actual delivered power required to raise a given volume of tissue to 45 degrees, (3) what is thermal distribution generated in- vivo (rat model), and (4) evaluation of thermal couple monitoring and feedback control mechanism for the system. The information obtained in Phase-I will be used to develop a more complete system in Phase-II aimed at more advanced animal and clinical testing.