Mediterranean Sea water inflow into the Black Sea is investigated using acoustic and oceanographic data obtained in the Black Sea exit region. The path of Mediterranean water and the resulting spreading on the continental shelf are observed with multibeam echo-sounding (SWATH) bottom bathymetry measurements, high-resolution echo-sounding images, and conductivity-temperature-depth profiles. It is found that the saline Mediterranean water is reduced by 6 practical salinity units as it flows and spreads on the shelf before reaching the continental slope, where it sinks to a depth appropriate to its density. Temporal and spatial variability in the flow and their relation to atmospheric and sea level changes are documented. It is shown that blockage of the Mediterranean undercurrent occurs when the estimated Black Sea water transport exceeds 25¿103 m3 s-1, which corresponds to a relative sea level difference greater than 40 cm. Mediterranean flow into the Black Sea is a high Reynolds, low Richardson number flow, resulting in a turbulent bottom boundary layer. Measurements of the path-averaged turbulent kinetic energy dissipation rate give values ranging from 1¿10-6 to 1¿10-4 W kg-1. ¿ 1999 American Geophysical Union