We have studied the reaction of 1-[2-(phosphonomethoxy)ethyl]cytosine (1) and its diisopropyl ester (2) with triethylammonium hydrogensulfite in 60% aqueous methanol. In the presence of some primary or secondary amine salts, at 25-70 °C, this reaction affords transaminated derivatives 4a-4e and 5a, 5b as main products accompanied by uracil compounds. However, with certain amines the reaction failed.