A double-blind, placebo-controlled trial of amantadine hydrochloride (Symmetrel) in acute herpes zoster (shingles) was carried out in 100 patients in general practice. The cases were serologically proved. There was no difference in duration of pain between the drug and placebo groups when pain disappeared during the 28 days' observation period. However, pain lasted more than 28 days in a significantly greater proportion of patients receiving placebo than of those on amantadine. Patients with pain after the 28-day observation period were significantly older than those whose pain disappeared during the study. The drug had no effect on rate of healing or appearance of new lesions.