Lithium chloride inhibited the replication of type 1 and type 2 Herpes simplex virus at concentrations which permitted host cell replication. Virus polypeptide and antigen synthesis were unaffected while viral DNA synthesis was inhibited. The replication of two other DNA viruses, pseudorabies and vaccinia virus, was inhibited but there was no inhibition of two RNA viruses, namely, EMC and influenze virus.