In the modern drug discovery process, a key step is to understand the mechanism of action of potential drug and its effect on the biological target. The cutting edge aproach to identify biological target of a potential drug is chemical proteomics, especially photoaffinity labeling of potential drugs. 3-(Trifluoromethyl)-3-phenyldiazirine group (TPD) proved to be the most appropriate way for this kind of labeling, since molecules with that functionality when illuminated with UV light (~360 nm) create a carbene which is reactive intermediate and forms a covalent bond with a biological target with which it is in close contact. In order to test this type of finding of biological targets and compare it with other affinity techniques used in proteomics, that do not produce a covalent bond between protein targets and the examined molecule, photoaffinity group was introduced to two known inhibitors of the epidermal growth factor receptor (EGFR) – lapatinib and erlotinib. The introduction of TPD functionality that is important for photoactivation and the formation of the carbene as a reactive species is done on the part of the molecule for which molecular modeling established that will not disrupt the way of binding to the receptor. Additional modification, so-called dual tag, was introduced into the lapatinib to form a covalently bound protein-molecule complex that may be isolate and analyze directly from the cell lysate. In the case of erlotinib, alkyne functionality that was originally present on the molecule was preserved and erlotinib was used as a control molecule. In addition, molecules with amino and alkyne functionality suitable for affinity binding to a solid support were also synthesized. The synthesized molecules were tested in vitro to determine their effectiveness in inhibiting the biological target (EGFR) and were subjected to the interaction with the cell lysate with or without UV irradiation at 360 nm depending on the applied chemical proteomic technology. Bound proteins were isolated from cell lysates and identified by mass spectrometry. Experiments have confirmed that these techniques can identify the biological target since the "caught" protein with all the modified molecules was EGFR. In addition to these expected results that validate the method, several new proteins were identified that may be potential biological targets for these drugs. For the final confirmation that identified proteins are possible protein targets for lapatinib and erlotinib, additional validation experiments should be done. In this work was confirmed that chemical proteomics technology is a useful tool for identification and characterization of biological target of an active substance. Especially reliable tool is the photoaffinity labeling of the molecules using 3-(Trifluoromethyl)-3-phenyldiazirine group that compared to other affinity technologies has the advantage that the protein creates a covalent bond with its biological target and remains undamaged when UV light is used.