In a previous paper we demonstrated that HIV-1 survival in syringes was strongly associated with the volume of blood remaining and with the duration of storage at room temperature. The current study was performed to determine the effects of storage temperature upon the survival of HIV-1 inside syringes. At 4 degrees C, 50% of all syringes contained viable HIV-1 at 42 days of storage, the longest storage duration tested. At room temperature (20 degrees C), the last day that syringes with 2 microL of infected blood were positive was Day 21, and viable HIV-1 was recovered from 8% of syringes. The last day on which syringes with 20 microL were positive was Day 42, and viable HIV-1 was recovered from 8% of syringes. Above room temperature (27, 32, and 37 degrees C), the likelihood of encountering syringes with viable HIV-1 when periods of storage exceeded 1 week decreased to less than 1%. The temperatures at which drug injectors are likely to store their used syringes will vary according to climate, season, and circumstances faced by the injector. The survival of HIV-1 in contaminated syringes varied over a range of temperatures, and this may be a factor influencing the syringe-borne transmission of HIV-1.