The insoluble and soluble fractions of Dermatophagoides farinae proteins were extracted using 8 M urea solution (8 M urea, 4% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, 40 mM Tris base) and 0.1 M PBS solutions, respectively. The main bands in the soluble and insoluble fractions were separately excised from SDS-PAGE gels and were determination using LC-MS/MS.