The suppression of wind-generated ripples by natural films was investigated in an oval-shaped wind-wave tank filled with seawater. Experiments were performed over the water surface with and without natural films; the former were produced through aging and the latter was assured through overflowing. Time series of the water surface slope were obtained with a computer-interfaced matrix camera system to determine the slope spectra. The inception of waves by wind was much delayed over the slick surface, while at higher winds there were insignificant differences between the mean square slopes over clean and slick surfaces. At low winds, suppression of ripples by natural films was observed from the intrinsic wave frequency of about 7 Hz and up, with the maximum suppression at about 19 Hz. No obvious spectral dip was observed to account for the Marangoni effect observed by others over artificial slick surfaces. ¿ American Geophysical Union 1992