The Finite Difference Time Domain (FDTD) method is applied to industrial microwave ovens used in the food industry. Theoretical and practical aspects of FDTD analysis for this purpose are dealt with. Two different open-ended applicator types are described and analyzed numerical ly and experimentally and their relative performance is discussed. One of these applicators is a novel design based on low impedance TM modes which reduces edge-overheating and load reflections. It is shown that the common belief that the heating pattern from open-ended microwave applicators can be predicted from their radiation fields alone is often in error, and that resonances in the whole system of applicators and food loads are of major importance.