The kinetics of 3′-azido-3′-deoxythymidine phosphorylation with [32P]orthophosphoric acid was studied in the presence of various coupling agents. The most effective method, with the use of BrCN, provided the isolation of the target 3′-azido-3′-deoxythymidine 5′-[32P]monophosphate in 46% yield and with high specific radioactivity (100 Ci/mmol). © 2005 Pleiades Publishing, Inc.