Nationally synthesized chemopreparations: phosphonoacetic (PAA), phosphonoformic (PFA) acids and acycloguanosine (Acg) exhibit a marked antiherpetic effect in cell cultures and marked protective effect in herpes meningoencephalitis in mice induced by intraperitoneal inoculation of herpes simplex virus type 1 (HSV-1) (43% PFA, 33% PAA, 25% Acg). Both in vitro and in vivo (mouse meningoencephalitis), PFA (its trisodium salt) on the whole proved to be less toxic than PAA but exerted a higher or similar antiherpetic effect. The combined use of pyrophosphate analogues (PAA, PFA) with Acg is more effective that their use separately both in vitro and in herpes meningoencephalitis in mice an produces an additive effect or one similar to it. Systemic inoculation of interferon inducers, lafarine or ridostine, is effective in herpes meningoencephalitis in mice induced by intraperitoneal inoculation of HSV-1 (the protective effect 33% and 26%, respectively). The combined use of ridostine and PAA in herpes meningoencephalitis in mice led to synergistic effect.