– 5′-Ethynyl-2′-deoxycytidine (EdC) functions as a nucleoside analog effectively inhibiting the replication of herpes simplex virus-1 (HSV-1) KOS strain with an ID50 of 0.2 μg/mL. Additionally, it decreases virus-induced cytopathogenic effects in PRK cells for HSV-1, HSV-2, and vaccinia virus strains, demonstrating MIC values between 0.2 to 5 μg/mL. EdC acts as a thymidylate synthetase inhibitor, selectively impacting the DNA incorporation rates of [1′,2′-3H]deoxyuridine compared to [CH3-3H]deoxythymidine in PRK cells with ID50s of 3 and 120 μg/mL, respectively. It further inhibits thymidine synthetase and curtails L1210 cell proliferation, a process reversible by deoxythymidine (ID50s are 4.4 and 1,000 μg/mL, respectively). Also, EdC is utilized in monitoring DNA synthesis and cellular replication through click chemistry conjugation, linking its ethynyl group with the azido group of various fluorochromes.