The diagnostic yield of sural nerve biopsy was evaluated in 120 peripheral neuropathy patients. In 58 (48%) a final diagnosis was reached without biopsy, while 14 (11.5%) remained undiagnosed. Nerve biopsy contributed to the final diagnosis in 20 of the 53 biopsies (38%). In patients with motor conduction velocity below 30 m/s, sural nerve histology was helpful in 65% of biopsies. In patients with milder reduction in conduction biopsy contributed in only 11%. It is concluded that in general neurological population, nerve biopsy is of limited value as a routine diagnostic procedure. However, in patients with marked slowing of conduction velocity, in whom the diagnosis is not immediately apparent, sural nerve biopsy is indicated.