The effectiveness of topical applications of capsaicin (truns-8-methyl-N-vanillyl-6-nonamide) in relieving pain was studied in 50 patients with a 2-month to 19-year history of postherpetic neuralgia unresponsive, or poorly responsive, to oral analgesics, antidepressants and neuroleptic agents. Of the 43 patients who completed the study, 70% experienced substantial relief of pain. Seven patients discontinued treatment because of a persistent burning sensation localized to the treated area.