Ribavirin, the only small molecule available so far for treating hepatitis C virus infection, was recently used in an emergency context to treat patients with severe acute respiratory syndrome in the early stages of the disease. EICAR, one of the most potent congeners of ribavirin, has 10 to 100 times greater antiviral potency than ribavirin. The mechanisms underlying the antiviral effects of ribavirin and EICAR have not yet been definitely elucidated, but they seem to be similar. In order to study the mechanisms responsible for their antiviral effects using a photolabeling approach, we have developed photolabeling probes of ribavirin and EICAR, in which an azido group was introduced into the pseudobases of triazole and imidazole, respectively. The ribavirin photoprobes were obtained by directly coupling the azidotriazole to the protected ribose sugar, while the EICAR probe was prepared by diazotizing AICAR and subsequently substituting with NaN3. All these probes showed a fast, clear-cut photochemical reaction, which suggests that they are promising tools for use in photolabeling studies.