Healthy normal volunteers between 18 and 65 years of age who have been exposed to cytomegalovirus are eligible for this study. Candidates will be screened with a medical history and blood tests. Those enrolled will provide a 30-milliliter (6-tablespoon) blood sample once a week for 4 weeks and a final sample 2 months later. The blood will be used to design a test to detect immune responses against CMV and determine the differences in these responses among healthy individuals.