The aim of this diploma thesis is to acquire basic knowledge about the closing mechanism of pores. The influence of the forming temperature and the shape of the pore on the closing behaviour during a compression test were examined. Three types of pores were machined by drilling and turning which differ in shape, size and orientation with respect to the deformation direction. The samples were compressed in the Gleeble 3800 at different forming temperatures and at a constant strain rate. Afterwards the samples were examined with a computer tomograph at the Austrian Foundry Research Institute and were evaluated with the program my VGL 2.2. This program offers, among other things, the possibility to evaluate the three dimensional shape of the pores. Some selected samples were analyzed by light microscopy and Electron Backscatter Diffraction to study the local orientation difference in the vicinity of the pores. The results of the tomography were compared with a finite element simulation. A clear influence of the forming temperature, the shape of the pores and their orientation on the closing mechanism was demonstrated.