An investigation of the hydrodynamic modulation of 1- to 3.5-cm wind waves in a wave tank is described. The modulation of short waves at wind speeds from 4 to 10 m s-1 was due to a mechanically generated 2-s surface wave. Measurement of the surface slope was obtained using a laser-optical slope sensor. The equilibrium height wave number spectrum was determined using the two components of the slope frequency spectrum. It was found to be consistent with k-3.75 cosp (&thgr;/2), where p is a decreasing function of k and wind speed. The linear modulation transfer function was found to be 2--3 times that predicted by a linearized action-conservation model based on Hughes' (1978) theory, and to increase with wind speed. Phase agreement is also unsatisfactory, the modulation being in phase with the oscillating current at high wind speeds. ¿ American Geophysical Union 1991