(2′S)-2′-Deoxy-2′-fluoro-5-ethynyluridine is a commonly used probe for DNA synthesis in vivo as it exhibits minimal impact on genome function in diverse tissue types. (2′S)-2′-deoxy-2′-fluoro-5-ethynyluridine is also ideally suited for metabolic DNA labeling when prolonged cell survival and undisturbed cell cycle progression are necessary, such as for pulse-chase experiments aimed at “birth dating” DNA in vivo.