The seismic magnitude of the October 2, 1969 high-yield underground explosion (Milrow) in the Aleutian Islands, when compared to the magnitude of the smaller 1965 Long Shot explosion, suggests that in the yield range near 1 megaton the yield exponent in the amplitude-yield relationship is significantly less than the value of unity which applies for yields less than 100 kilotons. The lower exponent is shown to apply equally well to Nevada Test Site high-yield explosions. A general Aleutian site effect is observed to produce seismic magnitudes for Aleutian explosions that are about m0.3 larger than those of similar-yield explosions at the Nevada Test Site.