In November 1999 and August 2000, the Infectious Diseases Society of America Emerging Infections Network (EIN) surveyed its members about shortages of antimicrobial agents in their hospitals and medical centers. Almost 90% of the members had encountered shortages of 1 or more agents in 1999. Of 496 respondents, 382 (77%) reported diminished supplies of penicillin G. Other agents in short supply included meropenem (38%), ticarcillin with or without clavulanate (24%), cefazolin (20%), gentamicin (50%), and nafcillin-oxacillin (13%). In 2000, 291 (60%) of 485 respondents reported shortages of penicillin G, but significantly fewer members had experienced a lack of other agents. In both surveys, members indicated that shortages had affected numerous therapeutic indications. In 1999, members estimated that shortages had affected thousands of patients. In 2000, they estimated that fewer patients were affected. The results of these 2 EIN surveys raise questions about the forces that govern the availability of these valuable therapeutic resources.