3'-Fluoro-3'-deoxyadenosine was active against a broad range of viruses, encompassing both DNA viruses [pox (vaccinia)], single-stranded (+) RNA viruses [picorna (polio, Coxsackie B), toga (sindbis, Semliki Forest)] and double-stranded RNA viruses (reo). Its antiviral activity spectrum, 3'-fluoro-3'-deoxyadenosine, clearly differed from those adenosine analogs known as inhibitors of S-adenosylhomocysteine hydrolase. 3'-Fluoro-3'-deoxyadenosine also proved effective in vivo in inhibiting tail lesion formation in mice inoculated intravenously with vaccinia virus[1].