The reduction of WC into W by reaction with a Hf-Cu melt has been found to proceed by the formation of layers of W and HfC. The extent of such incongruent WC reduction has been examined after the immersion of dense, polycrystalline WC plates in a vertical orientation in Hf-Cu melts at 1150-1300 °C for 1-24 h. A W layer of uniform thickness formed adjacent to the WC, whereas an irregular, but generally continuous HfC layer formed adjacent to the W layer. The rate of WC reaction was evaluated by measuring the thickness of the W layer as a function of reaction time, temperature and vertical position along the WC surface. Such kinetic data and microstructural analyses indicated that the incongruent reduction of WC in molten Hf-Cu is likely to be controlled by the diffusion of carbon through the W and/or HfC layers.