 Participants are admitted to the NIH hospital for 32 to 40 hours for a single 15-minute intravenous infusion of peramivir or placebo saline, followed by monitoring and evaluation. The drug dose is increased in successive groups of eight subjects; in each group, six subjects are given peramivir and two receive placebo. The first group receives 0.5 mgkg of peramivir; subsequent groups receive increasingly higher doses 1, 2, 3.5, and 5 mgkg as long as the last dose was well tolerated by the preceding group. Blood samples are drawn and subjects are monitored for vital signs temperature, blood pressure and heart rate and for symptoms such as headache, nausea, shortness of breath or pain at 0.5, 1, 2, 3, 6, 9, 12, 18 and 24 hours after the drug infusion. At the 24-hour evaluation they have an EKG. If needed, an echocardiogram ultrasound examination of the heart may also be done. Subjects return to the clinic 2, 3, 7, 14, and 28 days after the infusion for a check of vital signs, review of symptoms, blood draw, and urine sample collection. In addition, subjects are asked to collect all their urine for the first 48 hours after the study drug infusion. 