The ultrastructure of mast cells from the nine normal inferior turbinates were compared with those found in eight patients with perennial allergic rhinitis due to house dust mite allergy. Forty-six mast cells from normal patients were found in forty blocks and eighty cells were found in thirty-three blocks in patients with perennial allergy suggesting an increase of mast cell numbers in perennial allergy. There were no basophils outside the blood vessels and whole mast cells were found only in the submucosa. There was no difference in the morphology of cells of different sizes. Mast cells were more degranulated in the allergic mucosa. Degranulation, irrespective of cell size was found at all depths of the mucosa. A review of the literature covered the in vivo and in vitro descriptions of the ultrastructural morphology of human mast cells in the respiratory tract.