OBJECTIVES: The aim of this study was to measure the effects of past exposure to environmental tobacco smoke on the day-to-day dynamics of four respiratory-symptom classes in a diary study including adult never-smokers. METHODS: As part of SAPALDIA (Swiss study on air pollution and lung diseases in adults), a prospective multicenter cohort study, 1421 life-time adult nonsmokers were followed for 2 years with the use of daily questionnaires filled out during one to six periods of 4 weeks spread over 2 years (1992-1993). The hazard ratios (HR) of getting or losing respiratory symptoms from one day to another were determined in association with past exposure to environmental tobacco smoke. RESULTS: In a sample of adult never-smokers, an association between self-reported past exposure to environmental tobacco smoke and deteriorated average symptom dynamics was found for all of the outcomes considered, showing HR values from 1.09 to 1.21 for developing symptoms and HR values from 0.91 to 0.83 for getting rid of them. Exposure to environmental tobacco smoke, including the workplace, was negatively associated with the length of intervals without symptoms of bronchitis (HR 1.33) and asthma (HR 1.27), while exposure to environmental tobacco smoke confined to places outside work was positively associated with the length of episodes of any respiratory symptom and lower-respiratory-tract symptoms (HR 0.78-0.77). CONCLUSIONS: The results suggest that exposure to environmental tobacco smoke has adverse effects on the dynamics of respiratory symptoms, and the size (magnitude) and type of effects appear to depend on the place of exposure.