The binding of the trisaccharide, N,N',N"-triacetylchitotriose, to Urtica dioica agglutinin (UDA) was investigated using 1H NMR spectroscopy. UDA is a small antiviral plant lectin containing two homologous 43-amino acid domains. Carbohydrate-induced pertubations occur in one domain of UDA at trisaccharide concentrations below equimolar. Residues in the second domain are shifted at higher carbohydrate concentrations. This data confirms the presence of two binding sites of non-identical affinities per UDA monomer. Qualitative analysis of the 2D NOESY spectra indicates that UDA contains two short stretches of antiparallel beta-sheet. The 1H resonance assignments for both antiparallel beta-sheet sequences have been completed and there is one beta-stretch per domain. A number of these beta-sheet residues are perturbed in the presence of carbohydrate.