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Light cigarette (LC) exposure is supposed to be less hazardous with a decreased incidence of cancer and tobacco-associated diseases. C57BL/6 mouse groups were subjected to smoke from 3, 6 or 12 LC for 60 days and compared with mice exposed to ambient air (EAA) in order to study lung injury by morphometrical and biochemical methods. Bronchoalveolar lavage (BAL) analysis and histology and stereology were performed. Tissue from the right lung was used for measuring thiobarbituric acid reactive substances (TBARS) and Western blot analysis. One wayanova was performed followed by the Student–Newman Keuls post-test ( P < 0.05). The cellular content of BAL was 95% alveolar macrophages in all groups except in mice exposed to 3 LC, where 23% neutrophils were observed. Emphysema was not observed in three and 6 LC, but it was found in 12 LC parallel to increased volume density (Vv) of airspaces from 61.0 ± 0.6 (EAA) to 80.9 ± 1.0 (12 LC) and decreased Vv of elastic fibres from 17.8 ± 0.9 (EAA) to 11.8 ± 0.6 (12 LC). All exposed groups to LC showed low TBARS levels compared with mice EAA. Lung tissue from animals exposed to 12 LC showed decreased tissue inhibitor of metalloprotease-2 and increased matrix metalloprotease-12 detection, which suggests an imbalance in extracellular matrix (ECM). Increased tumour necrosis factor- α and nuclear factor- κB detection were observed in exposed groups to LC when compared with mice EAA. The data suggest that LC is so dangerous to lungs as full-flavour cigarettes inducing ECM imbalance and emphysema. [ABSTRACT FROM AUTHOR]