To the Editor. —Over the last several years, there has been increasing attention to the transmission of human immunodeficiency virus (HIV) through the sharing of equipment for the injection of illicit drugs. Intravenous (IV) drug users constitute the second largest group of persons to have developed acquired immunodeficiency syndrome (AIDS) in the United States and Europe and are emerging as the largest source of heterosexual transmission in both areas.1Although illicit drug injection is commonly associated with heroin addiction, it clearly is not the drug being injected that is responsible for the transmission of HIV. Cocaine injection may prove to be one of the more difficult aspects of preventing AIDS among IV drug users. Cocaine injection is quite common among persons who inject heroin—over 83% of the heroin users in our New York studies2had also injected cocaine in the previous two years. There is no chemotherapy for