Deoxyguanosine is a nucleoside consisting of the base guanine and the sugar deoxyribose. It is like guanosine, but with one oxygen atom removed. It is a nucleoside component of DNA. Deoxyguanosine can be converted to 8-hydroxy-deoxyguanosine (8-OHdG) due to hydroxyl radical attack at the C8 of guanine. 8-OHdG is a sensitive marker of the DNA damage This damage, if left unrepaired, has been proposed to contribute to mutagenicity and cancer promotion. Deoxyguanosine has long been recognized as a potent cytotoxic agent to cultured mammalian cells. This toxicity or inhibition of DNA synthesis by deoxyguanosine appears to be mediated by deoxyguanosine triphosphate-mediated inhibition of the enzyme ribonucleotide reductase. Purine nucleoside phosphorylase deficiency is thought to cause T-lymphocyte depletion by accumulation of deoxyguanosine and deoxyguanosine triphosphate, resulting in feedback inhibition of ribonucleotide reductase and hence DNA synthesis. Deoxyguanosine nucleoside analogs are potent antiviral agents.