We studied 2 patients from a Japanese family with familial amyloidotic polyneuropathy (FAP). Their clinical features are similar to type 1 FAP, and the proband's rectal tissue contained amyloid that stained with antihuman transthyretin (TTR) antiserum. Direct DNA sequencing of the proband's TTR gene revealed a guanine-for-adenine substitution in the second base of codon 42, producing a glycine for glutamate substitution in the plasma protein.