We used PCR to amplify proteinase activated receptor-2 (PAR-2) from human kidney cDNA. The open reading frame comprised 1191 bp and encoded a protein of 397 residues with 83% identity with mouse PAR-2. In KNRK cells (a line of kirsten murine sarcoma virus-transformed rat kidney epithelial cells) transfected with this cDNA, trypsin and activating peptide (AP) corresponding to the tethered ligand exposed by trypsin cleavage (SLIGKV-NH2) induced a prompt increase in cytosolic calcium ion concentration ([Ca2+]i). Human PAR-2 (hPAR-2) resided both on the plasma membrane and in the Golgi apparatus. hPAR-2 mRNA was highly expressed in human pancreas, kidney, colon, liver and small intestine, and by A549 lung and SW480 colon adenocarcinoma cells. Hybridization in situ revealed high expression in intestinal epithelial cells throughout the gut. Trypsin and AP stimulated an increase in [Ca2+]i in a rat intestinal epithelial cell line (hBRIE 380) and stimulated amylase secretion in isolated pancreatic acini. In A549 cells, which also responded to trypsin and AP with mobilization of cytosolic Ca2+, AP inhibited colony formation. Thus PAR-2 may serve as a trypsin sensor in the gut. Its expression by cells and tissues not normally exposed to pancreatic trypsin suggests that other proteases could serve as physiological activators.