Large urbanized areas, where sports events take place, have a polluted environment and can also reach high temperatures and humidity levels. The aim of this study was to investigate the impact of a hot, humid and ozone-polluted ( O3) environment on ( 1) performance of an 8 km time trial run, ( 2) pulmonary function, and ( 3) subjective respiratory symptoms in endurance-trained runners. Using crossover randomized design, 10 male participants (mean (V)over dotO(2max) = 64: 4 mlO(2) kg(-1) min(-1), SD = 4.4) took part in a time trial run under four different conditions: 20 degrees C + 50% relative humidity (rh) (Control), 20 degrees C + 50% rh + 0.10 ppm O-3 (Control + O-3), 31 degrees C + 70% rh (Heat), 31 degrees C + 70% rh + 0.10 ppm O-3 (Heat + O-3). Heart rate, ratings of perceived exertion and minute ventilation were collected during the run. Lung function was measured pre and post-exercise. The runners completed a respiratory symptoms questionnaire after each trial. The completion time of both the Heat (32 min 35 s) and Heat + O-3 (33 min 09 s) trials were significantly higher (P < 0.0001) when compared to the Control + O-3 (30 min 27 s) and Control (30 min 15 s) trials. There were no significant changes between pre/post lung function measures or between trials. The effective dose of ozone simulated in the present study did not affect the performance and therefore, ozone-pollution, at an environmentally relevant concentration, did not compound the impairment in performance beyond that induced by a hot, humid environment.