CMV retinitis is one of the most common opportunistic infections in patients with AIDS. DHPG is at present the only drug available for widespread compassionate use in the United States. Although most patients respond to treatment with DHPG, the medication does not cure the infection. Most patients will have a relapse and will require retreatment with DHPG. Because of the large relapse rate, most people treated for CMV retinitis are placed on continuous treatment with DHPG. There are two major problems associated with ongoing use of DHPG: 1) The development of a low white blood cell (WBC) count (leukopenia) which is a known side effect of the drug; and 2) the increased risk for leukopenia when DHPG is given together with AZT, the only antiviral drug currently available for the treatment of HIV infection. Therefore, patients cannot take both AZT and DHPG at the same time because the bone marrow toxicity is made much more severe when the drugs are given together. This has resulted in the difficult decision as to whether to forgo potential life-extending therapy with AZT in order to preserve sight. An effective treatment for CMV retinitis is needed that will allow the patient to also take AZT. ACV is presently the drug of choice for severe herpes virus infections. It has been shown to be effective in suppressing severe CMV disease in patients who have received bone marrow transplants.