Pregnant women were identified during the first trimester and followed monthly. Assessments were made of their smoking habits, urinary cotinine measurements, general medical condition, and status of pregnancy. Within two weeks of birth the infants were evaluated with partial forced expiratory flow-volume curves and measurement of passive respiratory system compliance and resistance. Measurements were repeated at intervals until age five. Babies were also observed regularly for respiratory illness experience, passive exposure to cigarette smoke, and general respiratory health.