The evaluation found that a medically supervised injection site staffed by nurses was well accepted among IDUs in the community. Homelessness was associated with frequent use of the SIF. Several of the variables associated with frequent SIF use had been previously associated with increased rates of HIV infection among IDUs in Vancouver. These variables included daily cocaine injection, daily heroin injection, and homelessness. Venous blood samples indicated that the hepatitis C virus prevalence was high in the sample at 88 percent. The HIV prevalence among SIF users was 16 percent, which was lower than HIV levels reported previously among the neighborhood's IDUs. Prospective followup of SIF users will be useful in examining blood-borne disease incidence and increases in medical care and addiction treatment. The SIF rule that prohibits nurses from assisting with injections is apparently undermining SIF use by IDUs who require help with injections. This is a significant issue, since this subpopulation of IDUs has been associated with increased rates of syringe sharing and HIV infection among Vancouver IDUs. Between December 1, 2003, and July 30, 2004, 713 SIF participants consented to enroll in the Scientific Evaluation of Supervised Injecting. Of these participants 43.2 percent used the SIF daily at the time of their baseline interview. The interview focused on participant characteristics and factors associated with reports of daily SIF use at the time of the baseline interview. Within the SIF, IDUs are provided with sterile injecting equipment and emergency care in the event of overdose, as well as primary medical services. Addiction counselors are available. 2 tables and 24 references