To investigate the characteristics of high-ozone occurrences in the Greater Seoul Area(GSA), three high-ozone episodes were selected, for which the ozone warning for concentration above 120 ppb might be issued. The selection was on the basis of morning wind directions and speeds, and daily maximum ozone concentrations measured between 1990 and 1997. The episodes chosen to meet selection criteria were seven days in July 1992, nine days in July 1994, and three days in August 1994, as respectively characterized by southwesterly, easterly, and calm winds in the morning. However, more than 80% of high-ozone days in the GSA were associated with calm winds and the concomitant accumulation of local emission in the morning, rather than being due to transport of ozone or its precursors. This is believed to be the primary reason why ozone concentrations in the GSA varied in a completely different manner even between adjacent monitoring stations. Several premises for initiating research studies for resolving these local variations of ozone concentrations in the GSA are also discussed.