Vertical gradient electromagnetic sounding (VGS) on the Endeavour segment of Juan de Fuca mid-ocean ridge reveals the presence of a 2D ridge-parallel, conductivity anomaly. If the anomaly is caused mainly by melt in a conventional upper mantle upwelling zone alone, then the conductivity of the zone is about 0.6 S/m. The corresponding Archie's law melt fraction exceeds 0.10. A significantly lower melt fraction requires a sheet-like, well interconnected melt. Upwelling zone conductivity can be reduced by a third if the anomaly is broadened and a crustal conductor is added to the model. ¿ 1998 American Geophysical Union