Summary. A technique to measure temporal variations of P and S body-wave attenuation is presented. Spectral ratios of earthquake doublets, recorded in the same station at different dates, are computed. Doublets are pairs of earthquakes which share the same hypocentre and magnitude; they have nearly identical wave forms and can be compared by using signal processing techniques. Three doublets were selected in the vicinity of the Coyote Lake, California, earthquake (1979 August 6, M = 5.9). The doublet following the Coyote Lake earthquake does not show any variation in spectral ratio. The doublet preceding the main shock by more than one year shows a small change in P spectral ratios and no change in S. The largest variation, in both P and S spectral ratios, is observed for the doublet whose first event occurred two months before the Coyote Lake earthquake. Despite the difficulty in completely eliminating source and calibration effects, the simplest interpretation of our data is to invoke temporal changes in P and S attenuation. P attenuation was significantly higher (by 8 per cent) and S attenuation larger (by 2-3 per cent), two months before the M = 5.9 shock than one year before and one month after. Such observations remind us of the possible role of the migration of fluids in the crust prior to an impending large earthquake and supports Aki’s plea for attenuation studies as a tool for earthquake prediction.