Summary:In 1986, community outreach workers began distributing small bleach bottles to injection drug users (IDUs) in San Francisco as a simple means for them to reduce their risk of infection with HIV and other pathogens by quickly flushing their syringes with bleach. At inception, the intervention was based on four assumptions: (a) sole reliance on expanded drug treatment capacity could not achieve HIV prevention goals, (b) legal barriers made syringe distribution or exchange schemes unfeasible, (c) IDUs would act in their own interest if the measures offered were acceptable to them, and (d) using bleach would diminish the risk of HIV transmission from reusing injection equipment. Following successful implementation of this program in San Francisco, similar programs were developed in many locations. These programs serve as the principal means of preventing needle-borne HIV infection among IDUs not enrolled in drug abuse treatment in the United States. Needed are definitive laboratory studies to determine the effectiveness of bleach decontamination as presently used by IDUs.