The objectives of this study are to: (1) to determine the prevalence of cytomegalovirus (CMV) infection and risk factors for infection in adolescent males; (2) to prospectively define the incidence and to evaluate risk factors for acquisition of CMV infection in adolescent males; and (3) to provide preliminary data on the duration and magnitude of CMV in the urine, saliva, and blood in those subjects who seroconvert during the study. Approximately 1000 males aged 12 to 17 years will be recruited from adolescent clinics at Cincinnati Children's Hospital Medical Center, Vanderbilt University, and the University of Texas Medical Branch at Galveston in order to obtain 225 CMV-seronegative subjects (75 at each site) to complete the Prospective Risk Factor Analysis. Patient participation will last a minimum of 24 months with 8 scheduled visits for the prospective seroepidemiology study. Patients who seroconvert will be invited to join the viral load analysis portion of the study, which consists of 8 scheduled visits during a 12 month period. The maximum duration of the study is 36 months, but will depend on the timing of seroconversion and entry into the viral load analysis. The study is divided into 3 parts: Seroprevalence, Prospective Risk Factor Analysis, and Prospective Viral Load Analysis. In the Seroprevalence portion of the study, after subjects have completed informed assent and parents or guardian consent, a small amount (10 mL) of blood will be obtained from subjects for evaluation of CMV antibody by commercial ELISA. Participants will be given a CMV fact sheet. Subjects will be contacted by phone with results of CMV antibody testing and the implications. They will be given the opportunity to receive the fact sheet again and discuss this information with study personnel, if they desire. Also at this visit, subjects who meet the eligibility criteria will be asked to complete a detailed questionnaire regarding possible risk factors for CMV infection. For those subjects 14 years of age and older, the questionnaire will include questions about sexual practices. Risk factors for CMV infection will then be compared between those subjects who are seropositive and those who are seronegative. Subjects who are CMV seronegative will be invited to participate in the Prospective Risk Factor Analysis portion of the study to determine the incidence of CMV infection and risk factors for acquisition in adolescent males. Eligible subjects will be identified and provided with a description of the study by a research nurse or study coordinator. Subjects will be asked to sign a separate assent and consent will be obtained from the parent or legal guardian. It is anticipated that recruitment will require approximately 1 year. Every 3 months, urine (For CMV culture and polymerase chain reactions \[PCR\]) and serum samples (for CMV antibody and PCR) will be collected from the subjects and analyzed for identification of CMV infection. In addition, subjects will complete a questionnaire evaluating risk factors at each 3-month visit. For those subjects who are 14 years of age or older, the questionnaire will include questions about sexual practices. If the subject tests positive for CMV, he will be asked to sign a separate consent to participate in the third phase of the study. In the Prospective Viral Load Analysis, subjects who seroconvert during the second portion of the study will be invited to participate in an evaluation of the duration and magnitude of CMV levels in blood, urine, and saliva. Subjects will be seen every month for 4 months followed by every 2 months for 8 months for collection of these specimens.