Blast furnace sludge is a heterogeneous material generated by the wet top gas cleaning process. It consists mainly of Fe, O, and C and contains major amounts of Si, Al, and Mg. Besides these elements, the sludge also contains trace metals such as Cd, Zn, and Pb. Reliable information about the total contents and distribution of the elements present in blast furnace sludge is of importance for hot metal production as some of them should preferably be recycled (Fe, C) and others (Cd, Zn, or Pb) are of environmental concern. Hence, the aim of the present study was to investigate the composition of blast furnace sludge with respect to the separation of desirable from undesirable elements. For this purpose, blast furnace sludge samples have been taken and analyzed with regard to particle size distribution (using wet sieving) and their respective contents of Fe, Zn, Pb, Cr, Ni, Cd, and C. The results of the analyses demonstrate that the concentration of the elements investigated significantly depends on the particle size. Coarser particles (>100 mu m) are characterized by higher contents of C, whereas fine grained particles (<20 mu m) show an enrichment of Fe and a significant accumulation of the heavy metals Zn, Pb, and Cd, which is attributed to their condensation on the particles' surfaces. The content of Cr and Ni in blast furnace sludge is largely independent of the particle size.