The association of mast cells with typical lesions of Kimura's disease was investigated by quantitative methods after immunohistochemical staining for Factor VIII-related antigen and counterstaining with toluidine blue. Formalin-fixed, paraffin-embedded, tissue sections from 9 confirmed cases of Kimura's disease were examined after staining to estimate mast cell and blood vessel densities by counting 100 random fields under oil immersion. There was a statistically significant increase of both mast cells and blood vessels in Kimura's disease (p<0.01) compared with normal skin and reactive lymph node controls. However, as far as the individual Kimura's disease lesion is concerned, there was generally no correlation between areas with mast cell increase and the degree of vascularity. Moreover, when lesions of less than 1 year's duration were compared with older lesions, there appeared to be a relative decrease in mast cells and a concomitant increase in vascularity in the latter. These results confirmed that mast cells are associated with Kimura's disease, and suggest that they may be involved in its early pathogenesis, although its possible role in angiogenesis may not be direct.