For treatment of viral infections due to herpes simplex virus (types 1 and 2) and varicella zoster (herpes zoster and chickenpox). Herpes simplex includes herpes keratitis, herpes labialis, and genital herpes. Acyclovir also improves the healing of herpes zoster lesions and reduce acute pain when given intravenously of by mouth. Beneficial effects may be more marked in immunocompromised patients.