Part I of this study, being done in the GCRC, is examining the safety, tolerance, and pharmacokinetics of rimatiadine by small particle aerosol. Part II of the study is an efficacy study. It will be a double -blind, placebo-controlled comparison of rimantadine by small particle aerosol. Part II of the study is an efficacy study. It will be a double-blind, placebo-controlled comparison of rimantadine by mouth and small particle aerosol in the treatment of acute influenza A virus infection.