The present paper aims to examine the application of night ventilation techniques to 10 urban canyons, situated in the extended region of Athens, Greece. As the climatic conditions in the urban environment frequently present important variation in different locations of the same urban area, the outdoor air temperature and the wind profile have been measured inside and outside the experimental canyons. The present work determines the impact of the urban environment on night ventilation energy performance, by studying a typical room located in the urban domain, under air-conditioned and free-floating operation, when single-sided and cross-ventilation are considered, during the night period. The influence of the urban microclimate on the efficiency of the technique has been examined by considering the typical zone inside the canyons and under undistributed conditions. The comparison of the results permits to evaluate the impact of the urban environment on the effectiveness of night ventilation techniques. The performed analysis shows that due to the increase in air temperature and the decrease in wind velocity inside the canyons, the efficiency of the studied techniques is significantly reduced compared with the situation that considers the undistributed conditions, dominating outside the urban canyons. (C) 2004 Elsevier B.V. All rights reserved.