Cases of pyogenic granuloma in pregnant women, nonpregnant women, and men were evaluated for the detection of estrogen and progesterone receptor proteins by immunoperoxidase staining. Immunostaining for estrogen receptors revealed a marked immunoreactivity of the endothelium within lesional tissue and in the overlying mucosal epithelium in many cases. Progesterone receptor immunoreactivity was only present within the epithelium, where it was much less than that of estrogen receptor immunoreactivity in both quantity (proportion of positive cells) and intensity. No characteristic staining pattern or significant quantitative difference among the three study groups could be discerned. These findings suggest that the quantity of estrogen or progesterone receptors in pyogenic granuloma is not the determining factor in the pathogenesis of this lesion. Rather, such a role may be attributed to the levels of circulating hormones. The levels of estrogen and progesterone are markedly increased in pregnancy and could therefore exert a greater effect on the endothelium of the pyogenic granuloma.