Transthyretin (TTR) isolated from amyloid fibrils from an Israeli patient ("SKO") with familial amyloidotic polyneuropathy has been studied by two groups of investigators. Originally, a position 49 Thr-->Gly substitution was reported; subsequently, a position 33 Phe-->Ile substitution was found instead. We have studied DNA from this patient by single strand conformation polymorphism analysis, restriction analysis, and DNA sequencing. On one allele, exon 2 contained both a T-->A transversion at the first position of codon 33, encoding the previously described Phe-->Ile substitution, and a G-->A transition at the first position of codon 6, encoding a Gly-->Ser substitution. The originally reported position 49 mutation was not encoded in the genomic DNA. This is the first report of a TTR double-variant allele in a patient with TTR amyloidosis.