Transthyretin isolated from amyloid fibrils from an Israeli patient with Familial Amyloidotic Polyneuropathy was sequenced by two research groups. One laboratory reported a position 49 Thr----Gly substitution, while the other noted a Phe for Ile interchange at amino acid 33. We used a transthyretin cDNA probe to study DNA from this patient by Southern blotting. The DNA displayed the unique Bcl I restriction site predicted by the mutation in codon 33. Because of the close size of the normal (6.40 kb), and variant (6.27 kb) fragments, the variant was more easily demonstrated after digestion with both Bcl I and Sph I, which generated two easily resolvable fragments of 2.39 and 2.27 kb.