Childrens' Respiratory Study of Tucson was also longitudinal in design and assessed the role of infectious, physiologic, immunologic, allergic, genetic, environmental, and familial factors in the development of acute and chronic lower respiratory tract illnesses in childhood. Enrollment of the study population and their families occurred between May 1980 and October 1984. Healthy infants were enrolled within a few days of birth, at which time baseline data were collected. Cord and 9-month bloods were evaluated for a number of immunologic tests. In the first few months of life, prior to any lower respiratory tract illnesses, a subset of the population underwent pulmonary function testing. During lower respiratory tract illness, specimens were obtained for viral, chlamydial, and mycoplasma cultures and tests. Environmental factors evaluated included passive smoking, number of siblings, overcrowding, and air pollution. Data collection was continued on the children and their family members over the years.