Carbon-13 n.m.r. measurements have been made in H₂O–D₂O solutions of cobalt(III) complexes containing an N-glycoside derived from ethylenediamine and an aldose (D-ribose or L-rhamnose). Partial deuteriation of exchangeable protons on the co-ordinated nitrogen atoms permits direct observation of the individual isotopomers and the resonances are observed as a series of multiplets, which can be analysed in terms of the two-bond and three-bond isotope effects that contribute to the deuterium-induced isotope shifts. The C–N bond formation between ethylenediamine and an aldose in the cobalt(III) complexes has been unambiguously confirmed by the information derived from the isotopic multiplets together with complete assignments of ¹³C signals from the sugar units by means of two-dimensional n.m.r. spectroscopy. An extra doublet originating from the four-bond isotope effect is observed for the D-ribosyl residue, which suggests that the sugar ring takes the furanose form. The importance of sugar ring oxygen atoms in the long-range deuterium isotope shifts is discussed including an examination by use of C¹-methine proton deuteriated aldoses.