This study deals with the serious pollution of Seoul's ambient air and extends a warning regarding its adverse effects on human health. The collected dust samples exceeded the legal standard (150 µg/m³ of total suspended particulates) of ambient air quality. Fine particles, with an aerodynamic diameter of less than 2.5 µm comprised on the average 75.4 percent of the total suspended particulates (TSP). The amount of ether extractable organic matter (EEOM) of the fine particles was found to range from 3.6 to 7.1 percent. Neutral, acidic and basic organics were fractionated. In the neutral fraction, aliphatic compounds (ALP), polyaromatic hydrocarbons0 (PAH), and polar neutral organic compounds (POC_N) comprised 23.1, 37.8 and 39.1 percent, respectively. Mutagenic activities of the organic fractions were determined by Ames bioassay. PAH showed the most mutagenicity using Salmonella typhimurium TA98 strain and TA98NR(nitro-reductase activity deficient stain) in the presence of S-9 fractions.