The role of spontaneous reporting in detecting the suprofen-associated flank pain syndrome was examined, including the specific effect of the "Dear Doctor" letter in accelerating the information-gathering process once the initial signal was generated. We believe this to be a noteworthy example of the ability of spontaneous reporting to produce a timely and unequivocal signal of drug-related risk. It also serves to demonstrate the need for vigilant postmarketing surveillance for all newly marketed drugs in the United States, even though considerable premarketing and postmarketing drug experience may exist from use in countries outside of the United States.