The invention describes an isolated nucleic acid sequence comprising the nucleotide sequence of SEQ ID NO:1 or a degenerate variant of SEQ ID NO:1. The nucleic acid sequence encodes an Ig-E binding immunogenic polypeptide the amino acid sequence of which comprises at least one sequence selected from SEQ ID NOS:4-25. The invention additionally provides an in vitro diagnostic test for detecting anti-cashew IgE in a patient. The test comprises reacting the patient's serum with a purified polypeptide the amino acid sequence of which comprises at least one sequence selected from SEQ ID NOS:3-25; separating the polypeptide from unreacted patient serum; reacting the polypeptide with a labeled human IgE-reactive agent after separating from unreacted patient serum; separating the polypeptide from unreacted labeled human IgE-reactive agent; and detecting labeled human IgE-reactive agent bound to the polypeptide after separating from unreacted agent to thereby indicate presence in the patient's serum of anti-cashew IgE.