We carried out a randomized double-bind, placebo-controlled clinical trial on the topical treatment of recurrent mucocutaneous herpes with a strong water solution of Ascoxal, an ascorbic acid-containing pharmaceutical formulation with mucolytic and non-specific antimicrobial activities. The lesion was firmly pressed with a cotton wool pad soaked in drug solution 3 times for 2 min with 30-min intervals on the first day only. Evaluation of the effects was by daily recordings of several different symptoms, including the presence and severity of erythema, induration, papulae or vesicles and scab by both the patient and a trained nurse, and by virus culture. Fourteen episodes with active treatment and 18 with the placebo were analyzed. According to the patients' records, the active treatment resulted in a significantly smaller cumulative number of days with scab (P < 0.01), or with any remaining symptom (P < 0.02) and significantly fewer occasions of worsening of any symptom after the treatment (P < 0.05). According to the nurse's records, the persistence of scabs was significantly shorter in the active treatment group (means 3.4 vs 5.9 days, P = 0.03). Virus culture after the first day of treatment yielded herpes simplex virus significantly less frequently in the active treatment group than in the placebo group (P < 0.01). In conclusion, a brief treatment with this ascorbic acid-containing preparation resulted in statistically significant clinical and antiviral effects, which calls for further and more extensive studies with a more intensive treatment schedule.