A single double-blind study conducted with 55 volunteers showed clearly that Exp 126 (alpha-methyl-1-adamantanemethylamine hydrochloride, rimantadine hydrochloride), an analogue of amantadine hydrochloride, reduced the occurrence and severity of artificially induced Asian influenza in humans. The infection (or seroconversion) rate in the drug-dosed and placebo-dosed groups was almost 100%, although the increase in serum neutralizing antibody levels was significantly less in the Exp 126-dosed subjects. The infecting influenza virus was recovered only from placebo-dosed controls. Probable untoward reactions from the drug occurred in three volunteers. Two related drugs, amantadine hydrochloride and rimantadine hydrochloride are now available for the prevention of Asian influenza.