Abstract: Disclosed is an anti-viral agent against varicella-zoster virus or cytomegalovirus comprising, as an active ingredient, 2-thio-5-halogenopyrimidine arabinoside of the formula (1): ##STR1## wherein B denotes a thiopyrimidine base of the formula (2) or (3): ##STR2## where X denotes a halogen atom; or ##STR3## where X denotes a halogen atom; and wherein each of R.sup.1, R.sup.2 and R.sup.3 is a hydrogen atom or a hydroxyl protecting group.

Abstract: An antitumor agent comprising (i) at least one pyrimidine type nucleic acid derivative having the general formula (I): ##STR1## wherein X represents a fluorine atom or a trifluoromethyl group, R.sup.1 and R.sup.2 may be the same or different and represent a hydrogen atom or an acyl group, R.sup.3 represents a hydrogen atom or a hydroxyl group, and(ii) at least one 1-[(2-hydroxyethoxy)methyl]uracil derivative having the general formula (II): ##STR2## wherein Y represents a hydrogen atom, a halogen atom, a methyl group, a benzyl group, a benzyloxybenzyl group, a vinyl group, a nitro group, or an amino group and R.sup.4 represents a hydrogen atom or an acyl group.

Abstract: An antitumor composition comprising a pharmacologically effective quantity of an ester of 1-.beta.-D-arabinofuranosylcytosine-5'-phosphate represented by the general formula ##STR1## where R is a monovalent aliphatic hydrocarbon group having 14 to 23 carbon atoms, and A designates a hydrogen atom or a pharmaceutically-acceptable alkali cation, and a vehicle is effective when administered by a non-injection method, particularly orally.