Thymidine (deoxythymidine; other names deoxyribosylthymine, thymine deoxyriboside) is a pyrimidinedeoxynucleoside. Deoxythymidine is the DNAnucleoside T, which pairs with deoxyadenosine (A) in double-stranded DNA. In cell biology it is used to synchronize the cells in G1/early S phase.