There is a clear risk for development of AIDS in hemophilic patients. AZT administration has been shown to inhibit HIV replication in vitro. Patients taking AZT have experienced fewer opportunistic infections and improvements in measures of immunity. The most common laboratory abnormalities observed with AZT are hematologic. However, the clinical and laboratory toxicity of AZT remains poorly understood in hemophiliacs. Hepatitis and liver dysfunction are more common in this population compared to other groups at risk for HIV infection. Because AZT is largely metabolized in the liver, drug pharmacokinetics needs to be evaluated in this patient population.