The potential for drug interactions leading to adverse reactions is great in patients with the acquired immunodeficiency syndrome, since multiple drugs are commonly prescribed to these patients. In addition, patients with acquired immunodeficiency syndrome have a higher incidence of adverse reactions to drugs that are commonly used in the treatment of opportunistic infections than non-acquired immunodeficiency syndrome patients. As a result of the high rate of adverse reactions, drugs that are currently available are often limited in their use. An appreciation of the potential drug interactions and knowledge of the most frequently occurring adverse reactions can increase the chance of a successful therapeutic response.