People engaged in agriculture, waste collection and other professions are exposed to large quantities of bioaerosols associated with organic dusts, ranging from 10³-10¹⁰ cfu/m³. These bioaerosols are composed of Gram-negative rod-shaped bacteria, Gram-positive, non-branching bacteria (corynebacteria, cocci and endospore-forming bacilli), actinomycetes and fungi (moulds and yeasts). Endotoxin produced by Gramnegative bacteria causes non-specific, inflammatory reaction in the lungs of exposed people, while thermophilic actinomycetes and moulds are a common cause of allergy. So far only little is known about health effects of Gram-positive bacteria, which in many cases form a dominant fraction of dust-borne bioaerosols.