A Hungarian family with familial amyloid polyneuropathy (FAP) was studied. The disease presented in two individuals with carpal tunnel syndrome in the fourth and fifth decades of life. The proband subsequently developed vitreous opacities requiring vitrectomy and now has evidence of cardiomyopathy. Single strand conformation polymorphism analysis and direct DNA sequencing revealed a variant AGC (serine) codon at amino acid position 84 of the amyloid precursor protein, transthyretin (TTR). The same single amino acid substitution in TTR was detected in an Indiana kindred with Swiss/German origin. Six individuals of the 11 tested being at risk for FAP proved to have the mutation in the present Hungarian kindred. This is the first description of this TTR gene mutation in Europe. Despite TTR gene haplotype analysis which suggests that the Hungarian and Indiana kindreds may have a common origin, no genealogical link has been identified between the families living in Indiana and Hungary.