Abstract: It has been discovered that 3′-azido-2′,3′-dideoxyuridine (CS-87) induces a transient mutation in HIV-1 at the 70th codon (K to R, i.e., lysine to arginine) of the reverse transcriptase region of the virus. Based on this discovery, a method and composition for treating HIV is provided that includes administering CS-87 or its pharmaceutically acceptable salt or prodrug to a human in need of therapy in combination or alternation with a drug that induces a mutation in HIV-1 at a location other than the 70th codon of the reverse transcriptase region. This invention can be practiced by referring to the published mutation patterns for known anti-HIV drugs, or by determining the mutation pattern for a new drug.