Numbers of airborne microorganisms, fungi, Gram-negative bacteria, thermophilic microorganisms, endotoxins and dust have been monitored in resource recovery plants and composting plants. The work is still in progress, so this paper decribes only preliminary results. Only low levels (< 15 ng m−3) of endotoxins were found at all locations. Levels of microorganisms, fungi, Gram-negative bacteria and dust changed with quality of waste, activity in the plant etc. Levels of airborne microorganisms, endotoxins and dust could be considerably decreased in resource recovery plants if only waste of good quality, e.g. presorted materials, is handled. For composting plants the highest levels of airborne microorganisms were found during aeration, especially by indoor composting where levels of 8.3 × 105CFU of mesophilic microorganisms were found.