Transthyretin (TTR, prealbumin) is a 55 kDa protein which plays an important role in the plasma transport of thyroxine and retinol. Although the liver and choroid plexus are the two major known sites of TTR synthesis, several lines of evidence suggest the possibility of a separate ocular source of TTR. We report the presence of TTR mRNA in rat and bovine eye and of TTR in rat eye. Preliminary immunohistochemical data indicate that the retinal pigment epithelium is a major site of TTR immunoreactivity in the rat. While the functional significance of ocular TTR synthesis is unclear, TTR may be involved in the ocular translocation and processing of retinol. The finding of TTR synthesis in the eye may explain ocular involvement in the familial amyloidotic polyneuropathies.