Relatively cool and fresh water, originating from the Middle Atlantic Bight continental shelf, has often been found along the northwestern margin of the Gulf Stream. In this paper we present measurements of temperature, salinity, and velocity within subsurface filaments of entrained shelf water adjacent to the Gulf Stream. The data indicate that vertical mixing within and near these filaments is effected by double-diffusive processes and shear-induced turbulence. The measurements also reveal a complex velocity and hydrographic structure within the filaments and show that the character of individual filaments differed considerably. For example, the measured mean flow within two filaments was much slower than the current in the adjacent Gulf Stream, whereas a third filament appeared to be incorporated within the high-velocity region of the Gulf Stream. The most thoroughly sampled band of entrained shelf water exhibited temperature inversions and contained a slowly moving intrusion of warm water, presumably detached from the Gulf Stream. The estimated transport of shelf water within this band was roughly 7.2¿104 m3 s-1, comparable with the rate at which water is transported over the southern Middle Atlantic Bight continental shelf as estimated by a previous study. However, the transport of individual entrained shelf water filaments may vary considerably because of the significant variation in their currents and hydrographic composition. ¿ American Geophysical Union 1989