The concentration of airborne bacteria and fungi in public buildings is regulated by law in Korea. Levels are investigated during the moderate seasons, spring (March-May) and autumn (September-November), using a six-stage cascade impactor. Total concentrations of airborne bacteria and fungi range from 290 to 940 cfu Á m À3 and 330 to 540 cfu Á m À3 , respectively. The levels of airborne bacteria and fungi are significantly highest in a kindergarten building and lowest in an elderly welfare facility ( p50.05). The ratio of respirable to total concentration range from 30 to 40% for airborne bacteria and from 55 to 70% for airborne fungi but there is no significant difference among the public buildings examined ( p40.05). The mean ratios of indoor and outdoor concentrations of airborne bacteria and fungi are below 1.0 regardless of the fraction of particle size and building type. The indoor concentration of airborne bacteria and fungi do not correlate significantly with indoor temperature and relative humidity ( p40.05). However, this does have a significant positive correlation with CO 2 and the number of people per area of the sampling site ( p50.05), which implies that the activity of residents has considerable effect on the levels of both airborne bacteria and fungi.