Hourly ozone, NOx and VOC concentrations, measured during 2001-2003 summer periods, are analyzed in order to examine the interaction patterns between the major photochemical pollutants in Istanbul. 34 high ozone days throughout the summer periods of the three years are determined and examined in the study together with the meteorological parameters like temperature, wind and vertical structure of the atmosphere. The results show that high levels of ozone are observed mostly under anticyclonic conditions with relatively low wind speeds. High ozone days generally experienced maximum concentrations at afternoon hours and minimum concentrations are reached at rush hours due to NOx-titration by traffic emissions. High negative correlations with NOx up to -0.84 are observed at the Sarachane station while higher correlations for VOC species, up to -0.75, are calculated for Kadikoy station. Some individual episodes experiencing high ozone concentrations up to 310 mu g m(-3) in the early morning hours are also studied. It is found that decreasing inversion heights in the early hours of the day led to suppression of pollutants close to surface and thus, an increase in ozone concentrations was observed. Low wind speeds played a major role in the increase of pollution levels in the region. HYSPLIT model is applied to some particular episodes and the results show that the northeasterly transport to the region was dominant, especially in the early-morning maximums.