Serum transthyretin (TTR) levels have been reported to be reduced in Portuguese and Japanese patients with TTR V30M familial amyloidotic polyneuropathy and pre-symptomatic carriers of the allele as well as in the carriers of a number of other mutant TTRs. The only published report of serum TTR levels in Swedish TTR V30M carriers suggested that serum TTR levels were elevated in a small number of cases. Since Swedish V30M carriers have a lower degree of clinical penetrance than those from other countries we wished to determine if the reportedly elevated serum TTR concentrations and the lower clinical penetrance were part of a pathologic process that differed between the Swedish carriers and those of other ethnic groups. We compared the serum TTR levels, as determined by ELISA, in 42 documented Swedish TTR V30M carriers with 16 control individuals from the same geographic area in northern Sweden. Serum TTR concentrations in the controls were statistically significantly higher than in the TTR V30M carriers, which were in the same range as those in African-Americans carrying the TTR V122I allele. Thus, Swedish TTR V30M carriers have the same reduction in serum TTR as do other ethnic groups carrying the same or other TTR mutations.