[en] Bioremediation, the stimulation of the natural process of biodegradation, played an important role in the cleanup of the oil spill from the Exxon Valdez in Prince William Sound, Alaska. Since there were already substantial indigenous populations of oil-degrading microbes in the area, it was apparent that degradation was likely to be nutrient - not microbial - limited. Bioremediation therefore involved the application of carefully selected fertilizers to provide assimilable nitrogen and phosphorus to the indigenous organisms, with the intent to stimulate their activity and enhance their numbers. The authors show here that the indigenous microbial populations were indeed substantially increased, throughout the sound, approximately one month after wide-spread fertilizer applications in both 1989 and 1990. Furthermore, while oil-degrading bacteria made up a significant fraction of the microbial populations on contaminated beaches in September and October 1989, they had declined to less than 1 percent by the summer of 1990, suggesting that the microbial populations on the shorelines were returning to their prespill conditions