Human lung mast cells have been reported recently to contain small amounts of the elastolytic protease present in the neutrophil and implicated in the pathogenesis of alveolar wall destruction in emphysema. Since mast cells are numerous within alveolar walls, release of inflammatory mediators (and possibly elastase) by cigarette smoking could contribute to alveolar injury in this disease. We therefore examined bronchoalveolar lavage (BAL) fluid for the mast cell granule constituents histamine and tryptase. The results, while not conclusive, supported the possibility that cigarette smoking increases secretion of histamine releasing activity by alveolar macrophages with subsequent degranulation of local mast cells. Mast cell discharge of inflammatory mediators (including neutrophil chemotactic factors and perhaps the elastolytic protease) could then participate in the destruction of alveolar walls.