Phytoncides are natural antimicrobic substances of plants. Some plants are able to form special biologically active agents which kill or suppress growth of pathogenic bacteria, microscopic fungi and microorganisms. Characteristic representatives of phytoncides are the essential oils extracted from vegetable raw materials by industrial methods. Phytoncides — one of factors of natural immunity of plants. The most powerful phytoncides to contain in a fir, a pine, a juniper, a birch, a poplar, onions, garlic, a horse-radish, a tutsan and in many other plants.