During the Shuttle Imaging Radar-B (SIR-B) mission of October 1984, synthetic aperture radar (SAR) images were taken off the coast of Japan. Wave spectra derived from SIR-B imagery were compared with simultaneous wave buoy observations. Waves at the time of flight were nearly perpendicular to the SAR flight direction and were composed of two major systems: a swell of about 200-m wavelength and wind waves with 70-m wavelength. Both the swell and wind wave peaks were identifiable in the SAR image spectrum after stationary response correction. Peak frequencies derived from SIR-B images and from the wave gauge agreed satisfactorily. However, the relative magnitudes of the peaks are not in accordance with the surface measurements. Possible reasons for the disagreement are discussed. ¿ American Geophysical Union 1988