We have determined that the duration of survival of HIV-1 in syringes typically used by injectors of illicit drugs can exceed 6 weeks. The percentage of syringes with viable virus varied with the volume of blood remaining in the syringes and the temperature at which syringes were stored. These experiments underscore the need for needle exchange programs and other HIV prevention interventions that promote the availability of clean syringes and the removal of potentially infectious ones from circulation.