A series of derivatives of the antibiotic 1-β-D-arabinofuranosylfhymine (ara T) was synthesized by esterification of the hydroxy group in the 5′-position of the arabinose moiety of the nucleoside with straight-chain and branched-chain carboxylic acids: acetyl-ara T, butyryl-ara T, valeroyl-ara T, pivaloyl-ara T and palmitoyl-ara T. These ara T prodrugs were evaluated for their effect on growth of L5178y mouse lymphoma cells and noninfected BHK-21 cells as well as for their antiviral activity in Herpes simplex virus type 1 and 2 infected BHK-21 cells. All compounds exhibited a marked antiherpes virus activity, whereas the cytostatic activity of two of them, the pivaleric ester and the palmitic ester, was extremely weak. The relative antiviral indices of the 5′-pivaloyl-ara T and 5′-palmitoyl-ara T were found to be much better than the index of ara T itself.