The stability of the major adduct formed between the endogenous product malondialdehyde (MDA) and deoxyguanosine, a pyrimidopurinone termed M1G-dR, was tested under a variety of conditions required for nucleic acid manipulation. M1G-dR was found to be stable at neutral pH and 37°C but to be unstable when stored at -20 °C in the presence of Tris buffers. A new product with a characteristic absorption band at 350 nm was identified by 1H-NMR as an enamino-imine comprised of one molecule of Tris, one molecule of MDA, and deoxyguanosine. The formation of the conjugate was observed on reaction of Tris with M1G-dR or its ring-opened derivative N2-(3-oxo-1- propenyl)deoxyguanosine. The Tris-M1G-dR conjugate was unstable in aqueous solutions at room temperature, undergoing hydrolysis. However, the Tris conjugate of M1G base remained stable at room temperature in organic solvent. The isolation and properties of a conjugate between M1G-dR and Tris suggest that cross-links may form by reaction of MDA with DNA but they are likely to be unstable to hydrolysis.