We studied the analgesic efficacy of an intravenous infusion of lidocaine and morphine in 19 adults with well-established postherpetic neuralgia in a three-session, randomized, double-blind, placebo-controlled trial. Compared with saline placebo, both lidocaine and morphine reduced pain intensity. Reductions in pain did not correlate with side effects produced by the infusions. For morphine, there was a significant correlation between reductions in pain intensity and blood level achieved. In the majority of subjects who reported definite pain relief, allodynia also disappeared. The results show that neuropathic pain can respond to opioids and to systemically administered local anesthetic drugs.