In both chronic and dermographic urticaria, superficial perivascular leukocytic infiltrations are seen histologically in lesional skin. We have therefore investigated the role of endothelial adhesion molecule expression in these diseases. E-selectin, P-selectin, ICAM-1 and VCAM-1 expression was examined immunohistologically, and the serum levels of the soluble forms of these adhesion molecules were determined by EIA in patients with chronic urticaria, dermographic urticaria as well as in healthy controls (n = 8 in each group) and subjects with symptomatic allergic rhinitis (n = 7) for comparison. A significant increase (p<0.01) was observed for soluble P-selectin in dermographic urticaria (mean 487+/-44 ng/ml) and chronic urticaria (mean 464+/-74 ng/ml) compared to healthy controls (mean 149+/-15 ng/ml) and rhinitis subjects (mean 177+/-30 ng/ml). In contrast, the other adhesion molecules were not significantly elevated in both urticaria groups. Immunohistologically, a strong expression of P-selectin was found in superficial vessels of lesional and nonlesional skin in dermographic urticaria with only a mild increase of the other adhesion molecules studied, supporting the findings observed with the soluble forms in the patients' sera. Since an alteration of soluble P-selectin was not seen in symptomatic allergic rhinitis, an unspecific effect due to inflammation appears to be unlikely. These results therefore point to a potentially relevant role of the endothelial P-selectin expression in the evolution of urticarial whealing.