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Workers spend considerable time in office buildings which are generally considered to be low risk environments. However, under favourable conditions (e.g. poor housekeeping, inadequate ventilation, poorly regulated temperature and relative humidity; nutrient substrates), indoor microbial levels may increase. Therefore indoor air quality (IAQ) becomes an important factor for workers health. This investigation examined air quality in offices situated one floor above the horse stables and evaluated the association with reported respiratory symptoms among office workers.Air sampling by impaction method onto agar plates was done for fungal detection. Fungi were identified using microscopy and BIOLOG system (metabolic fingerprinting). Environmental parameters (temperature, relative humidity, carbon dioxide) were measured using the IAQ monitor. Sampling was repeated (before and after cleaning intervention) in the offices near the horse stables (vaccine production). Employees completed a questionnaire on medical and occupational history.Air measurements showed high concentrations (155–1720 cfu/m3) of allergenic fungi. The most common genera isolated were Aspergillus, Penicillium, Fusarium, Trichoderma and Paecilomyces. The average fungal counts after cleaning the offices were threefold (954 cfu/m3) than before the rigorous cleaning process (303 cfu/m3). Office occupants complained of bad odour which worsened during the day. Symptoms reported by workers were nose irritation (60%), sinus congestion and headache (40%); and eye irritation and dry throat (30%). Symptoms worsened at work but improved when away from the office.Increased viable concentrations of airborne fungi in offices and high counts after cleaning indicated stables as a source of fungal contamination. The movement of horses between the stable and the paddock creates a lot of dust which is the likely mode of transmission to the offices. Some employees reported symptoms suggestive of those caused by the fungal genera identified. No complaints were received after the horse stables were relocated in keeping with local by-laws.