Introduction The study sought to determine whether mast cell counts in endobronchial biopsies of large airways are related to mast cell counts in the small airways.

Methods Lungs, obtained postmortem from 10 subjects who had died of non-respiratory causes, were fixed in inflation. Mast cell densities (cells/mm³), determined with an optical disector, were compared on histological sections (30 μm thick) of biopsies and small airways stained with human anti-mast cell tryptase.

Results Mean mast cell density over the inner airway wall in biopsies was significantly related to mean mast cell density over the total airway wall in the small airways (r=∼0.80, p<0.01). A minimum of three biopsies per case was required to demonstrate this relationship. Within relevant count areas, mast cell density was about 1.6-fold higher in the small airways than in the biopsies.

Conclusions These findings suggest that when mean counts from at least three biopsies per case are used, intersubject comparisons of mast cell density in the inner airway wall in endobronchial biopsies reflect intersubject comparisons of mast cell density over the total airway wall in small airways. This is despite the observation that mast cell densities are generally higher in the small airways.