We report ozonesonde observations from the following four locations across the United States: Trinidad Head, California; Boulder, Colorado; Huntsville, Alabama; and Wallops Island, Virginia. These ozone profiles clearly indicate evidence of stratosphere-troposphere exchange, boundary layer pollution, and strong seasonal variations. Significant variation at the shortest interlaunch frequencies (typically weekly) appears in all seasons, at all stations throughout the troposphere. Activity near the tropopause dominates in the winter and spring, while boundary layer ozone maximizes in the summer. The vertical extent and maximum values of boundary layer ozone are larger at the eastern stations. Comparisons to the TOMS overpasses indicate agreement to within 2% for the total-column ozone at all stations, with station-to-station mean biases less than 2%. The seasonal variation of the total ozone column is essentially identical at Trinidad Head and Wallops Island, while the summertime values at Boulder are significantly smaller by comparison, and the amplitude of the annual cycle at Huntsville is smaller than the amplitude of the other three stations. The longitudinal character of upper tropospheric ozone shows amounts generally increasing westward from Huntsville, and in the lower troposphere, ozone decreases westward from Huntsville in all seasons. Values to the east of Huntsville increase at all altitudes and seasons, with the possible exception of August when Huntsville's boundary layer and free-tropospheric ozone dominate.