Nearly complete sequence-specific 'H, I3C, and I5N resonance assignments are reported for the backbone atoms of the receptor-binding domain of vascular endothelial growth factor (VEGF), a 23-kDa homodimeric protein that is a major regulator of both normal and pathological angiogenesis. The assignment strategy relied on the use of seven 3D triple-resonance experiments [HN(CO)CA, HNCA, HNCO, (HCA)CONH, HN(COCA)HA, HN(CA)HA, and CBCA-(CO)NH] and a 3D "N-TOCSY-HSQC experiment recorded on a 0.5 mM (12 mg/mL) sample at 500 MHz, pH 7.0, 45 "C. Under these conditions, I5N relaxation data show that the protein has a rotational correlation time of 15.0 ns. Despite this unusually long correlation time, assignments were obtained for 94 of the 99 residues; 8 residues lack amide 'H and I5N assignments, presumably due to rapid exchange of the amide 'H with solvent under the experimental conditions used. The secondary structure of the protein was deduced from the chemical shift indices of the 'H", "CU, I3Cp, and I3CO nuclei, and from analysis of backbone NOES observed in a 3D I5N-NOESY-HSQC spectrum. Two helices and a significant amount of P-sheet structure were identified, in general agreement with the secondary structure found in a recently determined crystal structure of a similar VEGF construct [Muller YA et al., 1997, Proc Natl Acad Sci USA 9 4 7 192-7 1971.