Cobalt, being essential metal, influences different physiological and enzymatic functions. As cobalt does not accumulate in the body, Co-compounds have relatively low toxicity. The aim of the present study is the effect of complexes of Co(II) with aminoacids - lysine, arginine, histidine and serine on HSV-1 replication. No effect of [O2Co(his)4].nH2O and [O2Co(arg)2].nH2O on HSV-1 infection in vitro was found. Both, [O2Co(lys)2].nH2O and [O2Co(ser)2].nH2O suppress the attachement of HSV-1 particles onto target cells and the viral replication as well. Moreover, the properties of the particular Co-complex (charge, stability, structure) are manifestated by their virucidal effect. Thus, [O2Co(ser)2].nH2O irreversibly inhibits the infectious activity of free HSV-1 virions, while virucidal effect of [O2Co(lys)2].nH2O is completely reversible after the 2h of contact.