The Centers for Disease Control (CDC) has proposed revising the AIDS surveillance definition to include any HIV- seropositive person with a CD4 cell count of less than 200 cells per microliter. A study of persons receiving treatment for HIV infection indicated that this new definition would lead to an estimated 50-percent increase in the number of persons recognized as living with AIDS. Among 440 HIV-seropositive research participants recruited from drug treatment programs and through street outreach in New York City, 59 met this definition, but only 25 percent of those had been reported to the New York City AIDS registry. Therefore, the new definition, if combined with HIV and T-cell testing at drug treatment and street outreach programs, could produce very large increases in the number of injecting drug users meeting the new surveillance definition of AIDS. Tables and 12 references (Author abstract modified)