Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant inherited disorder. Recent biochemical studies have revealed that amyloid protein in FAP of Japanese, Swedish and Portuguese origin mainly consists of a variant transthyretin (TTR) (formerly called prealbumin) with one amino acid substitution of methionine for valine at position 30. In a 56-year-old man with typical polyneuropathy, gastrointestinal problems and vitreous amyloid, we diagnosed homozygosity for the TTR-met30-gene using RFLP analysis. In a family study, a sister presented the same homozygous RFLP pattern; however, in a careful clinical investigation we were not able to demonstrate any of the typical symptoms of FAP, nor could we demonstrate amyloid deposits in a biopsy skin specimen. This is the first report of homozygosity for the TTR-met30-gene, and it shows that the mutation of the protein involved in amyloid formation may be necessary but is clearly not sufficient for the clinical symptoms.