Thymidine (symbol dT or dThd), also known as deoxythymidine, deoxyribosylthymine, or thymine deoxyriboside, is a pyrimidine deoxynucleoside.

In its composition, deoxythymidine is a nucleoside composed of deoxyribose (a pentose sugar) joined to the pyrimidine base thymine.

Since thymine nucleotides are precursors of DNA (but not RNA), the prefix "deoxy" is often left out, i.e., deoxythymidine is often just called thymidine.

AZT inhibits the process of reverse transcription, a critical step in the viral life cycle.

It can be visualized by covalently binding a fluorescent azide using click chemistry, which is less harsh than the conditions used to expose the epitope for BrdU antibodies.

[4] A thymidylate auxotroph of the diploid yeast Saccharomyces cerevisiae was grown under conditions in which thymidyate levels varied from excess to depletion.