Syntheses of 5-(2-haloethyl)-2'-deoxyuridines, 5-(3-chloropropyl)-2'-deoxyuridines, and 5-(2-chloroethyl)-2'-deoxycytidine are described. The antiviralactivities of these compounds were determined in cell culture against herpes simplex virus types 1 and 2. All compounds were shown to possess significant and selective antiviralactivity. The most potent derivative, 5-(2-chloroethyl)-2'-deoxyuridine