Drug injection and syringe sharing is common among intravenous drug users in prison. Consequently, the prevalence of blood-borne viral infections is several-fold higher in prison than in the corresponding communities. Prisoners have been denied access to syringe exchange programs, even though they have been proven to be effective in community settings. A 12-month harm-reduction program that included syringe exchange was introduced into the only female prison (Hindelbank) in Switzerland. The program was studied for 12 months (pilot phase). Baseline data were collected on 137 of 161 inmates. Follow-up data were collected on 57 of 64 inmates. Participants were interviewed several times about their use and injection of drugs and their shared use of syringes. Additional data on the number of syringes exchanged were also collected. Reports of drug use and injection in prison did not increase. The exchange of syringes was related to drug availability. Frequency of drug use increased in relation to duration of incarceration. Frequency of drug use decreased the longer the project had been implemented. None of the main arguments raised against the introduction of syringe distribution into prison, such as assault or an increase in drug injecting, was evident in this study. The results, although limited by the nature and the size of the prison, suggest that syringe exchange has a role in the prison setting. 2 figures, 1 table, and 11 references