It compares demographic characteristics, injection and sexual behaviors, behavior modification, and HIV antibody status of IVDU's who inject only cocaine, IVDU's who use both cocaine and opiates, or IVDU's who inject opiates only. Results show cocaine only users or opiates only users are less likely than cocaine-opiate users to report high-risk, injection behaviors, although both result in some high-risk injection and/or sexual behavior. Also, cocaine and opiate users are more likely to have multiple sex partners than either cocaine or opiates users alone. Two-thirds of all study participants appear willing to modify their behaviors to reduce the risk of AIDS. Cocaine users either alone or with opiates are more likely to test positive for HIV infection than are opiate-only injectors. These data indicate that acceptable intervention programs would be used by the IVDU's. 14 references, 4 tables.