The purpose of this study was to examine the relation between development of respiratory symptoms and the rate of change in ventilatory lung function in young adults during a study period of 8 yr. The study population consisted of 391 subjects who were 15 to 40 yr of age at initial examination, when they underwent spirometry and an interviewer-administered ATS-DLD-78-A questionnaire on respiratory health, and who were reexamined 8 yr later. The association between the development of symptoms and the rate of change in FEV1 over time (delta FEV1, ml/yr) was studied in a linear regression model that included the potential confounders and other determinants of the outcome. The presence of modification by such factors as smoking, childhood exposure to environmental tobacco smoke, gender, or atopy was assessed by the significance of interaction terms between potential modifiers and incident symptoms. Subjects who developed wheezing and dyspnea and in whom a doctor diagnosed asthma had a significantly greater average annual change in FEV1 compared with those without respiratory symptoms or asthma (-12.3 ml/yr, SE 5.0; -16.2 ml/yr, SE 5.5; and -42.6 ml/yr, SE 11.5, respectively). When focusing on subjects without a diagnosis of asthma, the associations with appearance of wheezing and dyspnea remained significant. The associations were in general stronger in never smokers compared with smokers and were strongest in ex-smokers. The presence of atopy was a significant modifier, so that in subjects with atopy there was a stronger negative association between the onset of cough and asthma and delta FEV1 than in those without.(ABSTRACT TRUNCATED AT 250 WORDS)