Pterygia are considered to be induced by predisposing factors such as the external toxic environment. Glutathione transferases (GSTs) have a role in the detoxication of toxic chemicals. Transglutaminases (TGases) are involved in apoptosis, cellular adhesion and the wound healing process. As their expressions may be changed in abnormal conditions, we evaluated the clinicopathological status of pterygia by immunohistochemical study with GST-pi and TGase C. Twenty one pterygia, two pseudopterygia and five normal conjunctival specimens were used. The formalin-fixed samples were embedded in paraffin blocks, which were subjected to be stained with anti-GST-pi and anti-TG polyclonal antibodies immunohistochemically. They were graded from negative to strong. Staining patterns of GST-pi ranged from negative to weak in normal conjunctival epithelium, while in pterygia and pseudopterygia, one was weak, seven mild, ten moderate and five strong. As for TGase C expression, normal tissues were weak to mild, but ten were mild, nine moderate and four strong in pterygia and pseudopterygia. The general staining patterns of GST-pi and TGase C were prominent, ranged from moderate to strong in pterygia and pseudopterygia with basophilic degeneration and keratinization. On the corneal side of pterygia, TGase C was strongly positive in the basal epithelium on destroyed Bowman's layer and in conjunctival fibrous tissue. We suggest that GST-pi and TGase C are responsible for the process of pathogenesis of pterygia and pseudopterygia.