We report, for the first time, electrophysiological findings in the Finnish type of familial amyloidosis (FAF), a gelsolin-related form of systemic amyloidosis. Electromyography, nerve conduction studies, and blink reflex examinations were performed in 30 patients (age range 27-74 years). Cranial nerve involvement was detected in all, and peripheral nerve involvement in the majority of patients. Carpal tunnel syndrome was a characteristic feature of FAF, previously unrecognized. Myokymia-type short spontaneous bursts in frontal muscles were found in 3 younger patients. In addition to signs of axonal degeneration we found slow nerve conduction, prolonged distal motor latencies, and conduction blocks suggestive of demyelination. Most nerve conduction velocities correlated remarkably with age. We conclude that FAF is characterized not only by distinct clinical and molecular biological features but also by electrophysiological findings, which enable differentiation from other hereditary amyloidoses.