Objectives: This study determined the influence of exposure to environmental tobacco smoke (ETS) in aircraft on measured and perceived cabin air quality (CAQ), symptoms, tear-film stability, nasal patency, and biomarkers in nasal lavage fluid. Methods: Commercial aircrews underwent a standardized examination, including acoustic rhinometry, nasal lavage, and measurement of tear-film break-up time. Eosinophilic cationic protein, myeloperoxidase, lysozyme, and albumin were analyzed in the nasal lavage fluid. Inflight investigations [participation rate 98% (n = 39)] were performed on board four flights, two in each direction between Scandinavia and Japan. Scandinavian crew on six flights from Scandinavia to Japan participated in postflight measurements after landing [participation rate 85% (n = 41)]. Half the flights permitted smoking on board, and the other half, 0.5 months later, did not. Hygienic measurements showed low relative air humidity on board (2–10%) and a carbon dioxide concentration of <1000 ppm during 99.6% of the cruising time. Results: The smoking ban caused a drastic reduction of respirable particles, from a mean of 66 (SD 56) μg/m3 to 3 (SD 0.8) μg/m3. The perceived CAQ was improved, and there were fewer symptoms, particularly ocular symptoms, headache, and tiredness. Tear-film stability increased, and nasal patency was altered. Conclusions: Despite a high air exchange rate and spatial separation between smokers and nonsmokers, smoking in commercial aircraft may cause significant air pollution, as indicated by a large increase in respirable particles. This ETS exposure is associated with an increase in ocular and general symptoms, decreased tear-film stability, and alterations of nasal patency. (Authors' address: Department of Medical Sciences and Asthma Research Centre, Uppsala University, University Hospital, [email protected])