Farmers are usually exposed to a wide variety of noxious organic or chemical substances. This explains why agriculture is probably one of the occupations where prevalences of respiratory diseases are the highest. Some diseases such as extrinsic allergic alveolitis, allergic asthma, silo filler's disease or pesticides-related fibrosis are classic and well described. Others, more recently identified although probably more frequent, remain often unrecognized. This is notably the case of agricultural chronic bronchitis and of organic dust toxic syndrome. Sometimes, these respiratory pathologies are intricate and lead to a complex presentation where signs of irritation or inflammation of the respiratory tract, bronchial hyperreactivity and chronic bronchial obstruction are mixed.