The synthesis of 5-(azidomethyl)-2'-deoxyuridine (10) has been accomplished by two independent methods. The first involved tosylation of 5-(hydroxymethyl)-2'-deoxyuridine (1) to furnish a mixture of two mono- and a ditosyl nucleosides which were converted into the corresponding 5-(azidomethyl) (10), 5-(azidomethyl)-5'-azido (14), and 5-(hydroxymethyl)-5'-azido (15) derivatives of 2'-deoxyuridine. The second method was more selective and required the formation of the intermediate 5-(bromomethyl)-3',5'-di-O-acetyl-2'-deoxyuridine (8), followed by displacement of the bromo group by lithium azide and deacetylation. Catalytic hydrogenation of the azides 9, 10, 14, and 15 gave the corresponding amines 16, 2, 6, and 7, respectively. Compounds 1, 2, 10, and 16 inhibited the growth of murine Sarcoma 180 and L1210 in culture, and the activity of 2 was prevented by 2'-deoxypyrimidine nucleosides but not by purine nucleosides. The replication of herpes simplex virus type 1 (HSV-1) was strongly inhibited only by 1 and 10. Studies on the binding of the various thymidine analogues to HSV-1 encoded pyrimidine deoxyribonucleoside kinase indicate that 1 and 10 have good affinity for the enzyme.