A cDNA library corresponding to mite protein was screened using anti-Der f II, a major allergen from the house dust mite Dermatophagoides farinae, antibody. Three possible clones were obtained that contained cDNA fragments coding for Der f II, and the nucleotide sequences of the fragments were determined. There were minor differences observed affecting the deduced amino acid sequence among the three cDNA fragments. The amino acid sequence of the purified native Der f II protein could be analyzed to 45 residues from the N-terminus. As a result of comparison, all the three cDNA fragments code for a mature protein with a derived molecular weight of about 14,000. The amino acid sequence was not homologous to any known protein sequences and it contained six cysteine residues and no N-glycosylation sites.