Proteinase‐activated receptor‐2 belongs to a new subfamily of G‐protein‐coupled receptors. Its precise role during inflammation and the underlying mechanisms is still unclear. Our study establishes that PAR‐2 plays a direct proinflammatory role during cutaneous inflammation in mice and humans in vivo. In a model of experimentally induced allergic (ACD) and toxic (ICD) contact dermatitis (CD) we show that ear swelling responses, plasma extravasation, and leucocyte adherence were significantly attenuated in PAR‐2 null mutant (PAR‐2⁻⁷⁻) mice compared with wild‐type (PAR‐2^+/+) mice, especially at early stages. The proinflammatory effects by PAR‐2 activation were significantly diminished using nitric oxide‐synthase inhibitors, while NF‐kappaB and neuropeptides appear to play a minor role in these mechanisms. PAR‐2‐mediated up‐regulation of E‐selectin and cell adhesion molecule ICAM‐1;enhanced plasma extravasation was observed in humans and mice and of interleukin‐6 in mice in vivo. Thus, PAR‐2 may be a beneficial therapeutic target for the treatment of inflammatory skin diseases.— Seeliger, S., Derian, C. K., Vergnolle, N., Bunnett, N. W., Nawroth, R., Schmelz, M., von der Weid, P.‐Y., Buddenkotte, J., Sunderko¨tter, C., Metze, D., Andrade‐ Gordon, P., Harms, E., Vestweber, D., Luger, T. A., Steinhoff, M. Proinflammatory role of proteinase‐activated receptor‐2 in humans and mice during cutaneous inflammation in vivo. FASEB J. 17, 1871–1885 (2003)