Measurements of surface ozone were conducted at three remote island sites in the East Asian Pacific rim region during the Pacific Exploratory Mission-West (A) campaign period in September--October, 1991. The ozone concentrations observed at the three measurement stations at Oki and Okinawa, Japan, and Kenting, Taiwan, had similar ranges varying between 6--63, 8--58, and 4--65 ppb, respectively, except for one event of short-range transport of polluted air at Kenting. Day-to-day variations have been analyzed by using backward air parcel trajectories on isentropic surfaces. The results showed that continental air masses which originated from northwestern Asia and passed through the high anthropogenic emission region of East Asia contained the highest concentration of ozone, 30--60 ppb with an average of 43--45 ppb at the three stations. In contrast, the lowest concentrations were observed for air parcels originating from the mid-Pacific and transported without mixing with the continental outflow. These parcels contained 5--20 ppb of ozone with the average of 11, 15, and 9 ppb at Oki, Okinawa, and Kenting, respectively. The air parcels from the South China Sea contained 22 and 18 ppb of ozone at Okinawa and Kenting, respectively, which were higher than those from mid-Pacific. Continental air mass from the north-northeast to Oki containing 35--40 ppb ozone with the average of 37 ppb was recognized as continental ''background.'' The high ozone concentrations in the northwesterly continental outflow exceeding the background was ascribed to photochemical buildup in the planetary boundary layer. ¿ American Geophysical Union 1996