In this prospective natural history study, research was conducted on the response of the immature lung to Pneumocystis carinii and other opportunistic lung infections, as well as on the etiology and pathogenesis of lymphocytic pulmonary disorders. The types, incidence, course, outcome, and origin of cardiac disorders were also determined. In addition to the pulmonary and cardiovascular measurements, data on the effects of co-infection with other viruses, CMV and EBV, were obtained.