Influenza (flu) is a common respiratory infection and often causes severe illness. Few drugs are currently approved to treat influenza. This research will test the safety of an experimental anti-influenza drug called DAS181 that is given through an inhaler. The purpose of this study is to evaluate the safety of this new medication and how the body reacts to it. Any side effects will be measured by symptoms, physical examination or laboratory studies. About 27 healthy men and women age 18-45, who meet screening requirements, will participate. Three separate groups will be enrolled, with approximately 9 subjects in each group. Cohort 1:20 mg DAS181 or placebo for 1 day (total dose of 20 mg). Cohort 2: 20 mg DAS181 or placebo for 10 consecutive days (total dose of 200 mg). Cohort 3: 30 mg DAS 181 or placebo for 1 day (total dose of 30 mg.) Procedures include blood samples, electrocardiograms (measures heart activity) and breathing tests.