The reaction of acetaldehyde with deoxynucleosides was studied in buffered solutions at room temperature (22-24 degrees C) and neutral pH. Reaction products were obtained with all deoxynucleosides with the exception of thymidine, as shown by reversed-phase HPLC analysis. The order of reactivity was dGuo > dAdo > dCyd, for which three, two and one reaction products, respectively, were obtained. We report here data on the kinetics of the reactions, the stability of the adducts at physiological pH, product yields, UV-spectroscopic data at different pH values, and describe the synthesis, isolation and structural characterization by FAB/MS and NMR of the stable adducts of acetaldehyde with dGuo. Furthermore, the formation of adducts with dGuo by the cooperative reaction of Aa with ethanol was studied.