Proponents of needle exchange programs argue that a leading cause of hepatitis C and HIV is injection drug use and the sharing of contaminated syringes; given the difficulty of "curing" drug addicts, it is incumbent on public health officials to minimize the harm the user does by promoting the use of clean needles through needle exchange programs. Opponents of such programs argue that needle exchanges may increase illegal drug use, encourage non-injection users to become injectors, cause recovering drug addicts to relapse, increase crime in areas where needles are handed out, and send a message to youth that these programs condone illegal drug use. The limited research to date tends to undermine both arguments. A Seattle study and a Canadian study failed to show that needle exchange programs had any significant impact on the incidence of hepatitis or HIV, but the same studies also showed that the programs did no harm in areas where the drug epidemic was well established. One positive effect found from needle exchange programs was the increased likelihood that drug users involved in needle exchange programs would seek drug treatment. Future research should examine why some needle exchange programs seem to be more effective than others in reducing HIV transmission; how needle exchange should be coordinated with other HIV prevention efforts; what services should be provided in addition to an exchange program; and how exchange programs can be used to reduce hepatitis B and C among injecting drug users.