Summary The differential dignosis 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.

Summary Previous studies have shown that allergy to storage mites is a significant contributor to allergic disease among an isolated farming community in the Orkneys. The present study was undertaken to determine the prevalence of disease due to storage mites among farmers on the mainland of Scotland. Of the 290 subjects employed on 102 randomly selected farms studied, eighty‐seven (30%) reported allergic symptoms on entering barns or byres, and prick tests to storage mites were positive in 62 (21%). Rhinitis and conjunctivitis together were the more frequently reported symptoms, with less than half the subjects recording respitatory symptoms. Specific IgE antibody to storage mites was detected in 43% of subjects reporting allergic symptoms associated with hay dust. Specific IgE to storage mites was strongly associated with atopy in those subjects who reported allergic symptoms.

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Twenty-nine patients previously diagnosed as having suffered from farmer's lung in or before 1970 were asked whether the condition had recurred and what measures they had taken to avoid such recurrence. Those who had retired from farming had been least affected by recurrence, while those who continued to farm had been protected by making silage instead of hay or by wearing protective respirators. To be effective, a respirator should be worn on every occasion that farm dust is encountered and must be properly maintained.

Summary Fifty farming families on the mainland (the largest island) of Orkney were surveyed to assess the amount of allergic respiratory disease and the principal causative factor. This account deals with only type I allergy and demonstrates a prevalence of asthma and rhinitis of 17.3% and of extrinsic asthma and rhinitis, in which definite allergic causes can be identified, of 12.7%. In addition it is shown that over one‐fifth of the farming community are ‘atopic’ in that they demonstrate positive prick tests to one or more allergens. Less than 50% of those with allergic respiratory disease have attended the doctor with their complaint, a fact which calls in question the validity of epidemiological studies of allergic disease based on hospital and clinic attendances. Sex distribution confirms the finding that males suffer from asthma more frequently than females, however more females than males give positive skin tests without exhibiting symptoms of allergy. Pollens, animal danders and fungi all have a part to play in the aetiology of asthma and rhinitis among Orkney farmers, although the incidence of grass pollenosis is well below average. The two commonest allergens are hay dust and Dermatophagoides pteronyssinus which are found frequently to affect the same subject.