An array of six ocean-bottom seismometers deployed across a segment of the Mid-Atlantic Ridge recorded PKP phases from four teleseismic earthquakes. After correcting for normal moveout and elevation differences, there is a systematic variation of anomalous travel time with distance from the ridge. Stations at the ridge-axis are slowest. The average anomaly at a station 16 km from the axis is -0.36 s relative to the axial stations. Most of this anomaly is probably caused by the presence of partial melt beneath the ridge axis, perhaps concentrated primarily in the upper 30 km of the mantle. The rapid variation across-axis suggests that the melt is either associated with a narrow zone of buoyant upwelling or a region of veins and dikes forming a narrow transport zone connecting a deep melt-production region to the crust. ¿ American Geophysical Union 1996