Vertical ozone measurements were carried out in the urban environment of New Delhi, in three different seasons from 1989-1991. air sampling was done synoptically at ground level, 23 m, 51 m, 57 m, 117 m and 153 m heights. A significant positive vertical gradient in the ozone concentration was observed at all sites. At any given time, ozone levels were lowest at the ground level and invariably increased with increasing distance from the ground. A distinct seasonal variable variation in the vertical ozone profile was also observed. Ozone concentration was highest in summer at all heights. The peak in ozone concentration during the day, appeared earlier at all heights in summers, the ozone concentration decreased rapidly during the late evening. Such vertical ozone stratification may have severe implications for trees and residents of high rise buildings particularly in urban and industrial conglomerations which serve as the prime foci in the release of ozone forming substances.