Pharmacy operations on Guam during Operation Fiery Vigil are recounted. In June 1991 Mount Pinatubo, a volcano near Clark Air Base in the Philippines, erupted and forced the evacuation of the base's population. Some 20,000 military dependents were transported to Guam. Those evacuees who needed medical attention--some 2500 of them--were escorted to a temporary medical unit located in and around Andersen Air Force Base and consisting of Army, Navy, and Air Force elements. Full-service health care, including 24-hour pharmaceutical services, was available. A central pharmacy and four satellite pharmacies were established. The four-man pharmacy staff went on 12-hour shifts and made frequent trips to all the medical sites. The pharmacy established and maintained drug stocks and supplies and provided drug information, particularly information on therapeutic equivalents. Constant readiness for emergency drug requests was maintained, and the pharmacy was responsible for transporting drugs. The pharmacy also supported the Army Veterinary Service in processing, quarantining, and caring for 1300 pets. Cold, motion sickness, and sunburn preparations and analgesics accounted for more than half the prescriptions filled. Problems included the sheer number of evacuees, language barriers, the difference in formularies used by the pharmacies in the Philippines and Guam, and the physical and psychological stress to which the evacuees were subjected. Teamwork and coordination among the three U.S. military branches made it possible to satisfy the enormous medical and pharmaceutical needs of dependents evacuated from the Philippines after Mount Pinatubo erupted.