In this study, arsenic (As) and mercury (Hg) concentrations were determined in total suspended particulate matter (TSP) fractioned at nine different sizes (> 8, 8-6.5, 6.5-5.2, 5.2-3.5, 3.5-2.6, 2.6-1.7, 1.7-1, 1-0.43, and < 0.43 mu m) at five sampling stations (four urban stations and a background station) in Istanbul. A total of 80 TSP samples were collected using an Andersen 8-stage cascade impactor from July 2008 to August 2010. The mean As and Hg concentrations varied between 2.23 +/- 2.78 and 5.55 +/- 3.14 ng/m(3) and 0.59 +/- 0.09 and 1.25 +/- 0.10 ng/m(3), respectively. The highest total As concentration was measured at the AvcA +/- lar station, which is located in an industrial area. The lowest concentrations were measured at Kilyos station, which is a rural area of Istanbul. The highest enrichment factor (EF) values (> 10) of As were observed within the fine particle size (< 1 mu m) at all stations. The EF values of As generally decreased with increasing particle size. A significant negative correlation was observed between the size of the particles and the As concentration in the heating period at the BeAYiktaAY and Rasathane stations, which are located in residential areas. Higher Hg concentrations were found in fine particles (< 2.6 mu m) at stations near the sea, specifically during non-heating periods.