Abstract: Pleiotropic drug resistance (PDR) transporters play essential roles in cell resistance to various toxic compounds in various organisms including bacteria, mammals and yeasts. A large group of PDR transporters have been described in yeasts so far, including those that are controlled by transcription factor Pdr1p. Here, we show that besides their role in removing extracellularly added toxic compounds, the Pdr5p and Snq2p transporters play important physiological roles and significantly influence the developmental phases and physiology of yeast populations growing in a liquid culture. They appear to be involved in population quorum sensing, which consequently influences transcription factor Pdr1p level via feedback regulation.