The efficacy of r-interferon alpha 2a (IFM) versus acyclovir (ACV) and vitamin therapy in the treatment of herpes zoster is reported. A total of 305 patients were randomly divided into 3 groups. One million units of IFN were administered i.n. once a day for 6 days in 223 cases, oral ACV 200 mg five times daily for 7 days in 34 cases, and vitamin B12, B1 and B2 therapy at conventional doses for 7-14 days in 48 cases. The results showed that both IFN and ACV could reduce pain in patients with herpes zoster and cut the total duration of symptoms, in comparison with vitamin therapy (P < 0.01). In the IFN group, 45 patients (20.2%) experienced side effects, including mild fever in 35 cases (15.7%) and a slightly depressed leukocyte count or increased serum ALT level (3 cases each). In the ACV group, one complained of discomfort in the gastroenteric tract, and another patient reported lumbodynia.