We measured levels of airborne endotoxins in South Korea and compared these to PM10, PM2.5, and O3 levels in ambient environments; environmental factors affecting these levels were also analyzed. A total of 81 air samples were collected and analyzed using the kinetic Limulus Amebocyte Lysate (LAL) assay. The geometric mean was determined for the levels of endotoxins (0.132 EU m-3), PM10 (51.9 µg m-3), PM2.5 (22.6 µg m-3), and O3 (0.018 ppm). Endotoxin levels were significantly higher in the fall and winter as compared to summer. PM10 and PM2.5 were significantly higher, and O3 was by far the highest, in spring. Negative correlations were found between endotoxin and O3 levels (r = -0.491) and between endotoxin levels and temperature (r = -0.302). PM10 levels were also negatively associated with O3 levels and temperature but positively associated with PM2.5 levels. Given the negative relationship between airborne endotoxins and O3 determined here, further studies at larger sample sizes are needed to identify the mechanisms responsible.