Formaldehyde is an essential metabolic intermediate in human cells and can also enter into the body through environmental, exposures. It is classified as a human and animal carcinogen according to the International Agency for Research on Cancer (IARC). Previous research has demonstrated that formaldehyde is genotoxic, causing mutations in multiple genes. However, no exogenous formaldehyde-induced DNA adducts have been detected in animals after inhalation exposure, although formaldehyde can result in N-6-deoxyadenosine, N-2-deoxyguanosine, and N-4-deoxycytidine adducts in vitro. This can be partially attributed to the rapid metabolism of formaldehyde by glutathione (GSH)dependent enzyme systems. Among the intermediates in the pathway of formaldehyde detoxication, S-hydroxymethylglutathione is a reactive species and has the potential to further conjugate with DNA bases. Here, we have demonstrated the formation of S-[1-(N-2-deoxyguanosinyl) methyl]glutathione between glutathione and DNA in the presence of formaldehyde. This adduct is unique because of the involvement of S-hydroxymethylglutathione which is a key player during the detoxication of formaldehyde.