Zidovudine is the only anti-retroviral drug approved by the FDA for treatment of HIV infection. We have examined the clinical and laboratory efficacy of this drug for 4 years in a cohort of HIV-infected patients from Wisconsin. Overall, we have found that individuals with AIDS will have at least 1 year of symptom reduction while on the drug. Those with asymptomatic HIV infection tolerate the drug and none have progressed to AIDS in the 4 years of study. Zidovudine is an important component in the treatment of HIV infection.