In last decades the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging (MALDI-TOF MSI) has become an outstanding tool for detecting spatial distribution of different biomarkers in a variety of tissue samples. It utilizes the benefits of MALDI-TOF technique, which are rapid measurements of all mass spectra in a wide mass range and detection of analytes molecular weights. Moreover, the in situ identification of targeted biomarkers can be performed too. In our study, we focused on detection of metallothionein (MT) in chicken embryo. Metallothioneins are low-molecular weight proteins connected with cancer development and protection of organism against environmental pollution. Their main functions are detoxification of heavy metals, maintaining ion homeostasis and protection against the oxidative stress. According to our knowledge, nobody has done MALDI-TOF MSI of MT so far. Therefore, we have selected MT as our studied analyte not only because of this fact but also because a part of team IGA project is aimed on MT.