The immune system has the task of recognizing and identifying all foreign substances, which enter the body, as harmless or deleterious. There are a few cases were the immune system misidentifies a harmless substance as deleterious, thus invoking a hypersensitive response known as allergy. Amb. t. V, a small 40 residue protein with 4 disulfide bonds, elicits such an allergic response in a small human population. We have undertaken 2-D homonuclear studies, NOESY, jump-return NOESY, COSY, P.COSY, P.E.COSY, TOCSY, as well as 3-D homonuclear studies such as TOCSY-NOESY, and NOESY-TOCSY, of this small protein at 500 and 600 MHz. Using 3-D TOCSY-NOESY experiments we have identified unambiguously 3 of 4 disulfide bonds (C5-C35, C11-C26, and C18-C28). Using the 2 and 3-D data we have identified 438 NOE, 10 hydrogen bond, 62 torsion angle, and 37 J-coupling constraints. Structure calculations have been compared using three different methods: Distance Geometry/Simulated Annealing (DG/SA), quasi-relaxation matrix (to be published), and relaxation matrix refinement using the program X-PLOR 3.8. An ensemble of 19 structures has a RMSD for the backbone of 0.28 and 0.41 A for all atoms. The average r(1/6) value for this is ensemble 9.5%. NMR data, both NOE and J-coupling, is time and ensemble averaged data and thus contains information about the conformational variability of the molecular structure. We have performed ensemble averaging calculations and determined that the loop from residues 19 to 26 has two distinct conformations.