Transmission of HIV in IVDU's occurs primarily through contamination of injection paraphernalia with infected blood. Sharing of needles and syringes is common among drug users. The sharing of a vessel for injecting drugs is also common. Demographic factors are strongly associated with HIV infection for reasons not clearly understood. Members of ethnic minorities are overrepresented among both AIDS cases and HIV infection in IVDU's in the United States. Although IVDU's can transmit HIV infection through sexual contact, the primary mode of infection in addicts is needle use. This is shown in several studies on prostitutes that identify IVDU, not prostitution, as the primary risk factor for infection. Studies of heterosexual couples in which one or both partners are IVDU's have shown that heterosexual transmission to a non-drug-using partner is unusual; whereas, when both partners use drugs, concomitant infection is common. 20 references.