Lysine appears to suppress the clinical manifestations of herpesvirus infection. 45 patients with frequently recurring herpes infection were given 312-1,200 mg of lysine daily in single or multiple doses. The clinical results demonstrated a beneficial effect from supplementary lysine in accelerating recovery from herpes simplex infection and suppressing recurrence. Tissue culture studies have demonstrated an enhancing effect on viral replication when the amino acid ratio of arginine to lysine favors arginine. The opposite, preponderance of lysine to arginine, suppresses viral replication and inhibits cytopathogenicity of herpes simplex virus. The codons characterizing herpes simplex DNA apparently specify production of viral capsids at the expense of host cell histones.