Current meter moorings and high-resolution surveys in the Bosphorus reveal important details of the exchange flow. During early September 1994, the flow was quasi-steady and demonstrated strong mixing, particularly in the surface layer after it entered the principal contraction of the strait. Composite Froude numbers in the contraction are lower than expected, consistent with recent modeling that shows friction producing significant deviations from predictions of inviscid two-layer hydraulic theory. ¿ 1999 American Geophysical Union