Observations are presented of the benthic boundary layer (BBL) structure for two sites on the continental slope, west of the British Isles. Variability at the tidal (M2) and subtidal frequencies is discussed. A mean poleward, along isobath current is present at both sites, with periodic (5--8 days) reversals observed in the flow. These reversals cause a change in the water column stratification close (<100 m) to the seabed. The relationship between the direction of the along- and cross-slope flow, stratification, and the change of temperature in the frictional layer, relative to that above it, is consistent with Ekman veering induced up/downwelling close to the slope. The BBL temperature (density) structure is highly variable at the tidal frequency. There is a periodic variability in the current shear and associated Richardson number (Ri), particularly for the region where the bottom slope is close to critical for the M2 internal tide. Mixed or gravitationally unstable density layers are generated about one buoyancy period after the minimum Ri are observed. The mixed layers are transient, however, and do not persist throughout the tidal cycle. Indirect estimates of the vertical turbulent eddy diffusivity (Kv) were made from conductivity-temperature-depth (CTD) yoyo casts, and its variability through a tidal cycle measured. A background level of 10-4 m2 s-1 is estimated with high values O(10-2 m2 s-1) measured for the times associated with the generation of mixed or inverted density layers. A mean value of Kv=15--50¿10-4 m2 s-1 is found. The observations are compared to recent models of the sloping BBL and laboratory experiments, with particular emphasis on the transient nature of the BBL and the influence of internal wave reflection from the slope. ¿ American Geophysical Union 1994