In 6 healthy Haflinger horses stabled in individual boxes, different types of bedding (husk, straw and woodshavings) and hay (dry and soaked) were periodically changed. After each test period (45 days) bronchoalveolar lavage (BAL) was carried out for each horse, and the BAL fluid (BALF) withdrawn was submitted for citological and microbiological evaluation. The environmental dust burden was evaluated by means of an air filtration system and an optical counter with laser diode. Dust particles were sorted in eight size classes ranging from 0.3 to >20 mum. Qualitative evaluation of dust components was achieved by means of a Surface air system sampler (Sas). Total dust, which ranged from 0.03 mg/m(3) to 0.40 mg/m(3), prooved highly related with mast cell differential count (r = 0.61; P = 0.031. Besides, BALF mastcells differential count decreased significantly when hay was soaked. BALF alveolar macrophages showed a negative relationship with particles ranging from 1 to 2 mum (r = -0.55; P = 0.05) and from 2 to 5 mum (r = -0.61; P = 0.03), considered as respirable fraction (RF). It was concluded that even in healthy hones the investigated factors may play on important role in lower airways condition.