Various N-substituted benzisoselenazol-3(2H)-ones and their non-selenium-containing analogues have been synthesized and tested against selected viruses (HHV-1, EMCV and VSV) to determine the extent to which selenium plays a role in antiviral activity. The data presented here show that the presence of selenium is crucial for the antiviral properties of benzisoselenazol-3(2H)-ones since their isostructural analogues having different groups but lacking selenium either did not show any antiviral activity or their activity was substantially lower. The open-chain analogues of benzisoselenazol-3(2H)-ones--diselenides also exhibited high antiviral activity while selenides and disulfides were completely inactive towards model viruses.