Mast cells are traditionally recognized as round or oval connective tissue cells containing many specialized cytoplasmic granules. During recent years, more and more mast cell functions and properties have been clarified, and it is now evident that the mast cells are of different subtypes. The present study, utilizing chymase and tryptase immunofluorescence double-labelling and conventional electron microscopy techniques, has identified a kind of mast cells with obvious dendritic features in the lesional dermis of prurigo nodularis skin. This group of mast cell have enlarged cell bodies and contain fewer cytoplasmic granules, especially within certain dendrites. The morphological identification of such subgroups of mast cells could contribute to the understanding of mast cell heterogeneity.