We determined the major transport patterns for Bermuda and quantified the degree to which they influenced variability in ozone concentrations by applying cluster analysis to isentropic trajectories from September 1988, through September 1991. Concentration distributions of ozone associated with these transport patterns were significant different. The highest concentrations of ozone in each season were associated with transport off the North American continent; the lowest concentrations were during low-level maritime transport around the Bermuda high. Using the vertical component of the isentropic trajectories, we also showed that the most extreme concentrations of ozone occurred with rapidly descending air from midtropospheric levels. This pattern was most pronounced in April and May when more than 50% of the O3 variability was related to transport differences. We conclude that this relatively remote marine site, which normally experienced low maritime ozone levels (~30 parts per billion by volume (ppbv)), periodically entrained dry, ozone-rich (~55 ppbv) midtropospheric air in association with strong subsidence in high pressure behind spring low-pressure systems. Although the ultimate source of these midtroposphere, midlatitude, elevated-ozone concentrations is still being investigated, the synoptic meteorology associated with these transport patterns supports a significant contribution from the upper troposphere and lower stratosphere. ¿ American Geophysical Union 1995