A relationship has been suggested between mast cells (MCs) and male pattern hair loss (MPHL), because of histological evidence of perifollicular fibrosis and increased mast cell numbers. Two paired punch biopsies were taken from balding vertexes and non-balding occipital promontory areas of ten patients with MPHL (Ludwig-Hamilton IIIv to IV) and from five normal subjects aged from 20 to 35 years. Masson trichrome and Victoria blue staining were performed to observe collagen frameworks and elastic fiber structures. Numbers of immunoreactive MCs stained with anti-tryptase or anti-chymase antibody were counted. It was found that collagen bundles were significantly increased in balding vertexes than in non-balding occiput scalp skin. A near 4-fold increase in elastic fibers was observed in both vertex and occiput scalp skins with MPHL versus controls. Total numbers of MCs (tryptase-positive) in site-matched scalp samples were about 2-fold higher in MPHL subjects than in normal controls. Percentage elastic fiber (%) was found to be relatively well-correlated with tryptase and chymase-positive MCs. These findings suggest that accumulated MCs might be responsible for increased elastic fiber synthesis in MPHL, and indicate that future investigations are warranted.