Among the landmark discoveries of recent years are ribozymes, RNA molecules which possess enzymatic, self-cleaving activities. The concept of exploiting the ribozyme catalytic center for cleaving (inactivating) a specific RNA transcript is now emerging as a potential therapeutic or preventative strategy in human diseases, veterinary medicine and agriculture. Linked to the catalytic center of the ribozyme are RNA sequences which are complementary to, and thus serve to target the ribozyme to, a unique RNA sequence. Specific association of the ribozyme with its target via base pairing, cleavage of the RNA substrate and subsequent recycling of the ribozyme make these catalytic RNA molecules attractive as antiviral agents. Theoretically, ribozymes can be adapted for the destruction of any RNA species, whatever its origin.