Cathepsin W is exclusively expressed in immune cells, and a novel isoform was identified previously. To characterize the expression pattern of the wildtype and isoform Ins10, specific polymerase chain reaction assays were generated and used to study respective transcript levels in peripheral blood cells and gastric biopsies in healthy subjects. The wildtype-encoding transcript levels were 3- and 9-fold higher in mucosal samples and peripheral immune cells, respectively (p<0.05). The predominant expression of wildtype form by infiltrating immune cells was confirmed in 116 patients with gastroesophageal reflux disease and 27 reflux-negative individuals demonstrating that cathepsin W expression is not altered in this disease.