Genomic DNA from 17 Swedish patients with familial amyloidotic polyneuropathy (FAP), and 50 healthy controls were tested with a cDNA transthyretin probe. In seven of the patients, FAP was not reported in either of their parents. All 50 controls showed restriction fragments of 6.6 kb and 3.2 kb after cleavage with Nsil, while the 17 FAP patients showed RFLP markers of 5.1 and 1.5 kb. These observations indicate the same methionine for valine substitution at position 30 in Swedish patients with FAP as seen in patients with FAP from Japan, Portugal and FAP-patients of Swedish descent from USA. However, the mean onset of FAP symptoms for the 17 Swedish patients was found to be significantly later than for the patients from Japan, Portugal and USA.