Sick building syndrome is a term commonly used to describe the consequences of poor indoor air quality. It is well documented that first of all air quality depends on the chemical composition, and until now negligible attention has been paid to air pollution by microorganisms. Some species of fungi (Aspergillus flavus, A. fumigatus, A. niger, A. parasiticus, A. oryzea and other) and their toxins cause difficulty in breathing, allergic rhinitis, watery eyes, headaches, and flu-like symptoms. Over recent years considerable interest has been developed for plant extracts that would be of great use for the improvement of air quality. The biological activity of Pinus sylvestris L. has been investigated in order to find out its fungicidal activity against airborne microorganisms. It was determined, that fungi from Aspergillus and Penicillium genera dominated indoors. Antimicrobial activity of pine oil was evaluated by technique of oil diffusion to Czapek agar (for fungi), malt extract agar (for yeast and yeast-like fungi) and nutrient agar (for bacteria). Minimum inhibitory concentrations of pine oil to 13 species (8 fungi, 2 yeast-like fungi, yeast and 2 bacteria,) were determined: 1.0-2.5, 1.0-1.2, 0.5-0.75, and 0.75-1.2% (v/v), respectively. According to resistance to pine oil action, microorganisms grouped themselves as following: fungi, spore bacteria, yeast-like fungi, yeast, and bacteria (fungi being the most resistive and bacteria being the least resistive). The most active concentration of pine oil against all tested microorganisms was 2.5%, and the most sensitive fungus to volatiles was Ulocladium oudemansii.