This open label, randomized, three-period crossover study will evaluate the effect of co-administration of Tamiflu (oseltamivir) and rimantadine on the pharmacokinetics of Tamiflu and rimantadine. Healthy volunteers will receive multiple oral doses of Tamiflu, rimantadine or Tamiflu plus rimantadine in random order, with a minimum wash-out period of 7 days between treatments. Anticipated time on study is up to 11 weeks.