Kallikrein-binding protein (KBP) has recently been characterized as an endogenous inhibitor of kallikrein, and it is considered to be involved in several pathophysiological processes, such as hypertension. In the eye, its source has not been determined. We have investigated KBP mRNA expression in the ocular tissues of 5 Wistar-Kyoto rats using the technique of reverse transcription with polymerase chain reaction. Five cornea, sclera, iris, ciliary body and choroid samples were negative for KBP. Four retina samples were positive. KBP mRNA was more significantly expressed in the retina than in the other ocular tissues (p = 0.0238<0.05). Our present study demonstrates that KBP is synthesized in the rat retina, suggesting that KBP alteration may be involved in the retinal circulation.