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This study investigated the environmental conditions on pig farms and the respiratory health of pig farmers and their immunological response to airborne contaminants. Airborne concentrations of dust and ammonia were measured in 20 pig houses; viable microorganisms, endotoxins, and aeroallergens were measured in 6 of these houses, chosen to represent the range in dustiness. The 29 farmers employed on the farms completed a questionnaire and underwent lung function tests; 24 of them provided blood samples for the measurement of specific IgE and IgG antibody to extracts of pig squames and urine, feed components, and bacterial isolates. Mean airborne dust and ammonia concentrations in the pig houses ranged from 1.66 to 21.04 mg/m3 and from 1.50 to 13.23 ppm, respectively. Factors affecting these concentrations include time of year, feed systems used, and levels of ventilation. There was no direct relationship between airborne dust and ammonia concentrations. Airborne microorganisms ranged from 10(5) to more than 10(7) colony-forming units (cfu)/m3; most were bacteria, with few fungi or thermophilic actinomycetes isolated. Gram-positive bacterial genera (Staphylococcus, Micrococcus, and Bacillus spp.) predominated. Concentrations of endotoxin in collected airborne dust were low. Work-related respiratory symptoms, typically chest tightness/wheeze and nasal and eye irritation, were reported by 23 of the 29 workers. Three farmers had specific IgE to pig squames or urine and eight to feed components but none to the microbial extracts. Specific IgG to pig squames or urine and to feed components was demonstrated in 14 and 9 workers, respectively. Specific IgE responses occurred mainly in subjects with chest tightness or wheeze, although specific IgG responses were not related to symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)