Apoptosis is a special form of cell death, necessary for the development of an organism and maintenance of cellular homeostasis, that is the equilibrium between the loss and generation of normal-tissue cells during life. Hsp are the heat shock proteins which participate in several cellular processes, which are necessary for the normal growth and development of the cell itself. In the case of inhibition of Hsp90 the incorrectly folded proteins accumulate in the cell and the cell lacks the proteins to function normally. The transition of a cell to apoptosis is thereby induced. DMAG inhibits both α and β isomers, while siRNA is designed to destroy only α isomers. The aim of this thesis is to establish the apoptosis in THP-1 cells, of which some were treated with DMAG in various concentrations, and for some the mRNA level of cytosolic Hsp90 was silenced by RNA interference. The scale of cell death and apoptosis is determined by two methods, and those are cell coloration by Trypan Blue and TUNEL reaction. The TUNEL reaction has not identified any apoptotic cells, even not after repeated measurement. In the sample of THP-1 cells, coloured by Trypan Blue, which were treated by by siRNA molecules, and which was fixed after 24 hours, 77.6% dead cells were found. The percentage of dead THP-1 cells coloured by Trypan Blue increases with the DMAG concentration to which the cells had been exposed.