Biomass is widely used for fuel in developing countries. Particles and gases of biomass burning may cause changes in the lung. In this prospective study we investigated histopathological changes in the lungs of 42 non-smoking women [mean age (59 +/- 10) years] caused by biomass smoke. We valuated exposure to biomass smoke, case histories, and the findings of physical examination, radiology, bronchoscopy, and lung histopathology. Mean exposure to biomass smoke was (28 +/- 9) hour-year (1 hour-year equals 365 hours of exposure per year with average exposure of 1 hour a day). The radiological findings were mass (42 %), reticulonodular opacities (31 %), mediastinal lymphadenopathy (26 %), pleuro-parenchymal fibrotic banding (19 %), widening of the pulmonary artery (14 %), ground glass (11 %), mosaic perfusion (9 %), consolidation (9 %), segmental or subsegmental atelectasis (7 %), and bronchiectasis (7 %). The patients were diagnosed with lung cancer (35 %), interstitial lung disease (31 %), sarcoidosis (9 %), tuberculosis (9 %), chronic obstructive pulmonary disease (4 %), chronic bronchitis (9 %), and metastasis (4 %). Bronchoscopy showed pilies, oedema, erythema, bronchus narrowing, endobronchial tumour, mucosal irregularity, increased vascularisation, blue-black anthracotic plaques, mucosal oedema, and purulent secretion. Transbronchial biopsies revealed neutrophil and lymphocyte leucocytes in the perivascular, peribronchiolar, and interalveolar septa, slightly enlarged connective tissue, thickening of the basal membrane, thickening of interalveolar septa, intimal and medial thickening of the vascular wall and vascular lumen narrowing, anthracosis between the cells and in the bronchiole epithelium. These findings confirm that biomass smoke has important toxic effects on the lung parenchyma, interstitium, and pulmonary vessels that may result in malignancies.