Enrollment of participants began in May 1990 and continued through April 1993 in Group I and through January 1994 for Group II. The cohort was followed at specified intervals for an additional three years beyond the end of recruitment for clinical examination, cardiac, pulmonary, immunologic, and infectious studies and for intercurrent illnesses (The cohorts were followed through January 1997). Follow-up ranged from 2.5 to 6.6 years. The study ends in July 2002. Analysis of the database, preparation of manuscripts and follow-up of adult type pulmonary function studies in infants currently followed at sites conducting the Womens & Infants Transmission Study (WITS) continue through July 2002