The influence of many drugs of abuse – licit and illicit – on immune function has been examined extensively in recent years. Many such substances, including marijuana, cocaine, morphine, and nicotine, have been shown to enhance the disease process by impairing immunologic function. Use of these drugs impairs immunologic functions by suppressing antibody function, decreasing cytokine production, enhancing production and release of IL1, and suppressing IL2 and interferon. Among the viruses known to be effected by these drugs are viruses such as herpes simplex virus and murine retrovirus and bacterial agents such as Staphylococcus, Listeria, Treponema, and Legionella. This volume, part of the Infectious Agents and Pathogenesis series, examines a variety of drugs of abuse and how they affect the immune system.