Two trials of chlorprothixene were carried out, mainly on patients with moderate to severe post-herpetic neuralgia. When the drug was given as 50 mg b.d. to outpatients, unpleasant side-effects were more important than slight effects in alleviating pain. When the drug was given as 50 mg 6 hourly to inpatients for 5 days only, there was alleviation of constant chronic pain in a third of the patients; the effect is still lasting over a period of months in a few patients. The side-effects during the course of treatment are prominent. It is concluded that the drug is worth trying in the course recommended by Farber and Burks  when other means of controlling post-herpetic neuralgia have failed. It would be best to give the course only to inpatients.