A series of 8-substituted purine ribonucleosides were prepared from 2',3',5'-tri-0-acetyI-8-bromoadenosine and evaluated for cytotoxicity and antiviral activity. Four of these nucleosides (6b-9b) were significantly toxic to both HEp-2 and L1210 cells in culture but the most cytotoxic one (9b) was inactive against the P388 leukemia in mice. None of these nucleosides showed significant antiviral activity against Herpes Simplex 1 or 2, vaccinia, or influenza A. © 1994, Taylor & Francis Group, LLC. All rights reserved.