Spontaneous oto-acoustic emissions (OAEs) were measured prior to, during, and following administration of aspirin. The dose schedule was three 325-mg tablets every 6 h for a total of 16 doses (3.75 days). In every subject studied, all spontaneous OAEs gradually diminished and then disappeared during the drug regimen. Emissions that were initially small disappeared within 14-20 h of beginning the drug regimen (3-4 doses), while initially large emissions took 40-70 h (7-12 doses) to disappear completely. In contrast, the initial size of an emission appeared unrelated to the time required for it to recover to full strength once drug administration ceased. The recovery process was highly idiosyncratic, with the emissions of some subjects returning to full strength within 24 h, while for other subjects, full recovery required several days. In two subjects having multiple emissions in the same ear, the relative sizes of the different emissions often changed greatly during the disappearance and recovery phases. When small frequency shifts appeared for these subjects, they appeared--and were in the same direction--for each of the multiple emissions. In a related experiment, the spontaneous emission was unchanged in one subject who took a drug that inhibits the intracellular entry of calcium ions (verapamil).