During a cruise in September 1980 over the Blake Plateau we observed a northward spread of Antarctic Intermediate Water (AAIW) in the main axis of the Gulf Stream. The AAIW appeared as a lobe less than 60 km wide extending to at least 31¿N. The lobe was characterized by negative salinity anomalies of 0.15¿10-3, elevated nutrient concentrations, and lowered oxygen concentrations. Tentative evidence suggests that a parcel of AAIW was located over the central Blake Plateau, and geostrophic calculations indicate it may have been attached to the main Gulf Stream deep flow.