A 16 kDa buckwheat protein (BWp16) is a major allergen responsible for immediate hypersensitivity reactions including anaphylaxis. A deletion mutant of BWp16 (rBWp16DeltaN) was overproduced and purified and was shown to be immunologically active. A three-wavelength MAD data set was collected from a crystal of selenomethionine-labelled rBWp16DeltaN. The crystal belonged to the triclinic space group P1, with unit-cell parameters a = 28.39, b = 31.54, c = 32.20 A, alpha = 111.92, beta = 108.91, gamma = 98.74 degrees . One monomer was expected to be present in the asymmetric unit based on the calculated Matthews coefficient of 1.76 A(3) Da(-1).