To study the effects of amitriptyline in treating postherpetic neuralgia, 24 patients were randomly assigned to either drug or placebo in a double-blind crossover study. We found good to excellent pain relief in 16 of 24 patients (p less than or equal to 0.001). We did not find an antidepressant effect in most patients (p greater than 0.05). The median dose of amitriptyline was 75 mg. The median blood level was 65 ng per milliliter, and of nortriptyline 30 ng per milliliter. Good responses were maintained in 12 of 22 patients. Amitriptyline is useful in treating postherpetic neuralgia and may not act as an antidepressant.