Amyloidosis is characterised by the extracellular deposition of certain different proteins in a distinctively abnormal fibrillar conformation. All types of amyloid fibril share remarkably similar structural and biophysical properties despite substantial chemical heterogeneity among their respective precursor proteins. Hereditary amyloidosis associated with genetically determined protein variants is rare, but is extremely important as a model for studying the pathogenesis of amyloidosis generally. We report a novel mutation of the transthyretin (TTR) coding for TTR Ile73Val which is associated with familial amyloidotic polyneuropathy (FAP) in a Bangladeshi family. The mutation was detected by direct sequencing of the PCR-amplified TTR exons. It creates an additional AccI restriction enzyme site in exon 3, allowing confirmation of its presence by RFLP. Amyloid detected in sural nerve and colonic biopsies was shown to be composed of TTR by immunohistochemistry. The predominant clinical features were progressive autonomic and sensori-motor peripheral neuropathy, beginning at age 50years. The proband's father and two siblings had similar illnesses. These findings indicate Val73 is an amyloidogenic variant of TTR.