Abstract: Provided are methods for ventilating a surgical theater using temperature-regulated laminar air flow. Velocity of a downward directed laminar clean air flow is determined by an air-temperature difference between the supply air and room air temperature at the level of the operating table. Room air temperature at the level of the operating table is measured and clean supply air temperature controlled in relation to this measurement. In order to maintain a constant downward directed laminar clean air flow velocity, a constant difference in temperature is maintained between room air temperature at the level of the operating table and the lower temperature of the supply air. In preferred embodiments, this constant temperature difference provides a downward directed air flow velocity of at least 0.25 m/s and is maintained in part by minimizing fluctuations in ambient air-temperature through use of air supply units supplying heated or cooled air outside the clean air zone.