Systemic acyclovir (ACV), a new potent anti-herpes drug, was shown to reduce effectively the morbidity in the acute phase of herpes zoster ophthalmicus (AHZO). Using high dose oral ACV (5 X 800 mg/day) our aim in this study was: (1) to compare disease profiles in the ACV-treated group and in a group of zoster patients having had no ACV, analysed retrospectively; (2) to establish if high-dose ACV was able to prevent severe long term complications of AHZO; and (3) to determine the present role of corticosteroids in AHZO. From 1984 to 1988, 48 patients with AHZO of less than 3 days' duration were included. All patients received at least 7 days of oral ACV (5 X 800 mg/d) associated with topical ACV. Steroids were not given unless severe uveitis occurred. Follow-up was 2 years in 43 patients and 1 year in all 48 patients. Main conclusions from our study are: 1. Ocular involvement occurred in 67% of ACV-treated cases, a rate comparable to our retrospective group (59%) and to the literature (71%). However the rate of severe long term complications was minimal (4%) when compared to our non-treated retrospective group (21%). 2. Steroid treatment was not necessary in any of the ACV-treated patients. 3. ACV was well tolerated and did not have to be discontinued in any of the patients. High dose ACV and avoidance of steroids seems to eliminate the severe complications of AHZO.