A method of diagnosing atopy or a predisposition to atopy in an individual, which comprises demonstrating the presence of a mutation or polymorphism in a specific DNA sequence of a gene encoding the beta-subunit of the high affinity IgE receptor in the individual. Two variant DNA sequences linked with atopy are as follows: 5' GAA TTG GTA TTG ATG (SEQ ID NO: 2), 5' GAA TTG GTA GTG ATG (SEQ ID NO: 4), both commencing at nucleotide 5640 of the beta-subunit gene. The invention makes it possible for the first time to identify individuals at genetic risk of developing atopic illness.
