Rayleigh-wave spectral amplitudes generated by two United States nuclear explosions, Rulison and Rio Blanco, were equalized to epicentral distance of 10°, corrected for geometric spreading and instrument response, and filtered by a narrow-band filter to obtain corrected spectral amplitudes. The corrected spectral amplitudes were used in a least-squares scheme to evaluate the symmetric source radiation pattern parameters and average attenuation coefficients, as functions of frequency. The parameters are: the explosive source; the F factor, which is the ratio of the double-couple source to the explosive source; and the radiation pattern azimuth. The evaluated average attenuation coefficients were used, with the station epicentral distance to adjust the corrected spectral amplitudes to obtain the source spectral amplitude, from which the spectral magnitudes were calculated. The explosive source parameters of the radiation pattern and the spectral magnitudes, at different frequencies, were used to estimate the yields of the above two explosions. The estimated yields for the two explosions are within 2 to 6 per cent of the announced yields. The best yield estimate was obtained from the explosive source parameters which estimated the yields for Rulison at 40.6 kt and Rio Blanco at 88.6 kt. The announced yields for Rulison and Rio Blanco are 40 and 90 kt, respectively.