PURPOSE: To assess the relative distribution in the cornea of amyloid and beta ig-h3 gene product in lattice corneal dystrophy type IIIA (LCD-IIIA), METHODS: Serial sections from the cornea of a patient with LCD-IIIA were subjected to either Congo red staining or immunohistochemistry employing an antibody to beta ig-h3, Also, genomic DNA was isolated from peripheral blood and used as a template for polymerase chain reaction to amplify all exons of beta ig-h3, RESULTS: Exon 11 of beta ig-h3 was mutated (Pro501Thr), Subepithelial and intrastromal congophilic deposits exhibited a birefringency characteristic of amyloid, These regions of the tissue were also highly immunoreactive with the antibody to the beta ig-h3 gene product. CONCLUSION: Amyloid and Pro501Thr-mutated beta ig-h3 protein accumulate and colocalize in LCD-IIIA. (Am J Ophthalmol 1999;127:456-458. (C) 1999 by Elsevier Science Inc. All rights reserved.).