High-frequency regional records from small earthquakes (1.3P/Lg spectral ratios in the band 1--25 Hz are about 0.5 and 1.25 for earthquakes and explosions, respectively, in the eastern United States. We find that the high-frequency P/Lg spectral amplitude ratio in the frequency band 5--25 Hz is a reliable and robust discriminant for classifying these events. A linear discriminant function analysis indicates that the P/Lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1%. Single-hole instantaneous explosions and ripple-fired quarry blasts have somewhat different P/Lg spectral ratios, but as a group are distinctly different from earthquakes. ¿ American Geophysical Union 1993