The direct alkylation of adenine at the 3 position was extended to produce series of 3-alkyl-, 3-allyl- and 3-(substituted benzyl)adenines. When these compounds were tested for enzyme inhibition and antiviral activity in vitro, 3-n-pentyladenine was the most active compound in inhibiting the enzyme dopamine .beta.-hydroxylase, and 3-(2-bromobenzyl)adenine showed the most striking inhibition of multiplication of vaccinia virus and of herpes simplex virus in tissue culture [African green monkey kidney cells].