Cell-surface protease-activated receptors (PARs) appear to have evolved to detect extracellular enzymatically active serine proteases such as trypsin and thrombin. The predominant location of PARs on endothelia and epithelia and the discovery of enzymes such as trypsin within these tissues, together with the linkage of PARs to cytoprotective pathways, provide new information on autocrine and paracrine signalling within these critical barriers. In this article, the ways in which the distribution and function of PARs could be harnessed by pharmacologists as novel anti-inflammatory therapeutic strategies are discussed.