This experiment examined the efficiency of biological removal of air contaminants performed with a prototype “open” biofilter. The biofilter bed composed the following components by weight: 35% fibrous peat, 35% sallow peat, 10% barley straw, composts from sewage plant and horse manure -10% each. With Waters` liquid chromatograph use there was determined a content of ammonia, nitrates, nitrites, sulphates, chloride phosphates, iodides, bromides and fluorides in the air. The examinations on the physico-chemical properties of medium and air pollution were run over 180 days, collecting the samples on the 5^th, 35^th, 65^th, 95^th and 180^thbiofiltration days. After 35 days there was recorded stabilization of temperature, moisture, reaction, dynamic growth of total bacteria count and coli titre in the medium. Ammonia biofiltration efficiency ranged from 36 to 89%, while for nitrates, nitrites and phosphates it was even higher than 66-100%.