From a group of pyrrolo[2,3-d]pyrimidine compounds that have been screened against influenza virus, one derivative, 4-(3-piperidinyl benzylamino)-2-methyl-7H-pyrrolo[2,3-d]pyrimidine (9), has shown promising activity against both the A and B strains. The compound had activity comparable to amantadine, but was inactive when given orally. 4-(Substitutedphenyl ethylamino)-2-methyl-TH-pyrrolo[2,3 d]pyrimidines showed no improved activity.