SummaryAntiherpetic activity of AME was demonstrated in in vitro inactivation tests and in cell culture systems against herpes zoster and five strains of herpes simplex virus.The recently reported activity of water-soluble amphotericin B methyl ester (AME) against lipid-bound viruses (2, 3) suggested the potential use of this polyene antibiotic for topical treatment of herpetic infections. Extensive studies in our laboratories have shown significant antiherpetic activity with AME, as evidenced by the inactivation in vitro and by the inhibition in cell cultures of herpes zostervaricella and five strains of herpes simplex virus. Activity was independent of type or strain relationships among the viruses tested. Since host-cell membrane components of the lipid viral envelope have been proposed as the site of interaction with AME (3), it was essential for these comparative studies to prepare all strains of herpesviruses in the same host-cell line, the host of choice being MA-184 human newborn foreskin cells. The minimum effective concentration of AME necessary for maximum virueidal activity was limited by and directly related to the size of the virus population. While quantitative sensitivities were similar in most cases, a comparative analysis using two strains of herpes simplex virus showed different kinetics of inactivation for each strain. The present report deals ~dth these findings.Amphoteriein B methyl ester (AME) is a semisynthetie antifungal agent produced by esterification with diazomethane of the heptaene macrolide antibiotic, amphotericin B (5). Chemically, AME is a base which easily forms watersoluble salts with mineral and organic acids. In contrast, the parent compound Arch. ¥iroL 48/4 27