Immunopathology is recognized as an important component of infectious disease manifestations, and corticosteroids have been used as an adjunct to antimicrobial therapy for a variety of conditions. Antiviral therapy of herpes labialis has been shown to result in only a small reduction in the time to healing and the duration of pain. To determine if topical application of a combination product containing 5% acyclovir and 1% hydrocortisone (ME-609) could provide benefit to herpes labialis patients, 380 immunocompetent adults with a history of herpes labialis were exposed to experimental UV radiation (UVR) to induce a recurrence. On day 2, just before the appearance of the majority of lesions ("delayed" lesions), subjects were randomized to receive active medication or vehicle control six times per day for 5 days. Overall, 120 of 380 patients developed delayed classical lesions, of whom 50 of 190 (26%) had been treated with ME-609 and 70 of 190 (37%) had received placebo (a reduction of 29% [P ؍ 0.02]). Healing time, measured as the time to normal skin, was reduced by treatment with ME-609 (9.0 days for treated patients versus 10.1 days for the controls [P ؍ 0.04]). There was a trend toward a reduction in the maximum lesion size in the ME-609 recipients compared to that in the controls (43 versus 60 mm 2 , respectively [P ؍ 0.07]). The treatment had no effect on lesion pain, but ME-609 treatment reduced the number of patients with moderate or severe tenderness. Compared to treatment with a placebo, treatment with the combination antiviral-immunomodulatory cream provided benefit to patients with experimental UVR-induced herpes labialis, reducing classical lesion incidence, healing time, lesion size, and lesion tenderness. ME-609 is a novel product that merits further evaluation as a treatment for cold sores.Treatment of herpes simplex virus (HSV) infections with antiviral drugs has been a major challenge for investigators for more than 30 years. The benefits of treatment of recurrent HSV infection have been modest in contrast to the benefits of treatment of primary infection. The main clinical benefit in the treatment of recurrences has been the modest reduction in lesion healing time of approximately 10 to 15% (5, 10). Recurrent disease differs from the primary episode in that the virus is cleared much more rapidly, usually within 3 days or less. Although the immune response is quicker and more effective in controlling recurrent disease, it also may be responsible for most of the clinical symptoms, which persist for up to a week after the virus can no longer be isolated (6, 9). Thus, a combined modality of therapy aimed at both an antiviral effect and an immunomodulatory effect has been proposed in a number of studies (1, 9).The availability of a small-animal model for evaluation of the effects of treatment on the severity of recurrent lesions has been a limiting factor in evaluations of therapy. A novel animal model of recurrent HSV disease was recently developed by the use of zosteriform HSV infection in mic...