The degradation pattern of the N-oxides of various tertiary aminouridines is established. The N-oxide of 3'-deoxy-3'-morpholino-arauridine generated double bonds in the carbohydrate moiety without much selectivity, whereas epimino uridine N-oxides generated only d 4 U. Oxazolidine derivatives were formed from the N-oxides of 3'-deoxy-3'-N-pyrrolidino/morpholino-2,2'-O-anhydrouridines and 3'-deoxy-3'-N-pyrrolidino/morpholino-2'-O-mesylarauridines. 2'-Deoxy-2'-N-pyrrolidino/morpholino-2'-O-mesylxylouridines produced rearranged products 3'-O-N-pyrrolidino/morpholino-2,2'-O-anhydrouridines.