Abstract: The invention refers to antiviral and antitumor compositions which are useful for the control of viruses and tumors and which, in addition to a known antiviral or antitumor active xanthate, contain an adjuvant which increases its antiviral and antitumor action. The adjuvant is an ionic, preferably an anionic, compound with a lipophilic group and a hydrophilic group, preferably an alkali metal deoxycholate or a compound the lipophilic moiety of which is a straight or branched, saturated or unsaturated, aliphatic group with six to eighteen carbon atoms, and the hydrophilic group of which has one or two carboxyl, sulphate, sulphonate, or phosphate groups, or a pharmaceutically-acceptable salt thereof.