'Barn allergy': asthma and rhinitis due to storage mites.

The differential diagnosis of asthma in farm workers is between a type I hypersensitivity to a pollen or dust allergen and a type III hypersensitivity to mould antigens. We describe asthma and rhinitis, and not farmer's lung, in a farming population due to the non-pyroglyphid grain storage mite. Before a diagnosis of farmers' lung due to mouldy hay is made in any patient whether or not precipitins to Micropolyspora faeni are present, skin tests for storage mite should be made. If these are positive a diagnosis of 'barn allergy' should be considered and a trial of sodium cromoglycate be given.