The effect on the efficiency of power transfer and microwave leakage of different applicator-load coupling schemes is examined. For a 915-mHz applicator and musclelike phantom separated by 4 cm, it is found that by filling the air gap with dielectric powder or deionized water, the efficiency of power transfer from applicator to load can be raised to levels comparable to that obtained for direct applicator-load contact. For these coupling conditions, it is also found that microwave leakage intensities in the immediate vicinity of the applicator-phantom interface can be reduced to direct contact levels. Employment of such materials and techniques in our clinic, for coupling applicators to patient surfaces in the administration of local hyperthermia to head and neck tumors, has facilitated the reduction of average microwave leakage intensities from more than 15 MW/cm2 to less than 3 MW/cm2 in most cases.