Mast cells (MC) have been implicated in both normal and pathological angiogenesis, such as that in chronic inflammatory diseases and tumors. This assumption is partially supported by the close structural association between MC and blood vessels and the recruitment of these cells during tumor growth. MC release a number of angiogenic factors among which tryptase, a serine protease stored in MC granules, is one of the most active. In this study, we correlate the extent of angiogenesis with the number of tryptase-reactive MC in tissue fragments from pterygium and normal bulbar conjunctiva investigated by immunohistochemistry, using two murine monoclonal antibodies against the endothelial cell marker CD31 and the MC marker tryptase. Angiogenesis, measured as microvessel density, was highly correlated with MC tryptase-positive cell count in pterygium tissues. These results suggest that the characteristic neovascularization observed in pterygium may be sustained, at least in part, by MC angiogenic mediators, in particular tryptase.