Fibronectin (FN) is a glycoprotein present in the epithelial surface of airways and in the interstitial parenchyma of the lung. The aim of this study was to quantify the amount of FN in human lung parenchyma, and to investigate possible differences between smokers and non-smokers, both in lung parenchyma and in bronchoalveolar lavage (BAL) fluid. BAL fluid was recovered in 21 individuals. Quantification of FN in BAL was done by a non-competitive ELISA. Twenty-six lung parenchyma samples were also obtained from lung resections. FN was extracted with urea and heparin. Quantification of FN in lung parenchyma was determined by a competitive ELISA. The mean +/- SD FN content in BAL fluid from smokers was 1.59 +/- 1.65 micrograms/mg total protein and 0.53 +/- 0.26 in non-smokers (p < 0.05). However, the amount of FN/ml BAL fluid was not statistically different between smokers (0.15 +/- 0.13 micrograms/ml) and non-smokers (0.106 +/- 0.07). The mean extractable FN in human lung tissue was 38.6 micrograms/g wet weight (31.7-45.5, 95% mean confidence interval) with no statistical difference between smokers and non-smokers. We conclude that in smokers, FN accounts for a higher proportion of the total protein in BAL fluid, and that there were no differences in FN content in lung parenchyma between smokers and non-smokers.