This study will last approximately 6 years. Step 1 is the longitudinal screening phase of the study. Patients at high risk for CMV disease who are enrolled in the study will be screened every 8 weeks for CMV in the blood; medical history assessment, physical examination, and blood work will occur at each visit. Additional blood collection to monitor HIV infection will occur every 16 weeks. Patients will undergo opthalmologic examination every 24 weeks. Patients who develop detectable CMV in their blood during Step 1 then enter Step 2 of the study.