Certain hope is entertained in the prediction of chemosensitivity in vitro/ ex vivo for the purpose of selecting the most effective treatment of malignant diseases with minimal patient loading. The possible choice of an effective substance based on the results of a simple ex vivo test would increase the success of the treatment in case of standard chemotherapy failure or in the treatment of primary chemoresistant tumor. MTT test seems to be an easy process for the prediction of chemosensitivity of isolated malignant cells ex vivo, however each method represents a simple tool, which can provide false results if incorrectly preformed. Numerous limitations significantly reduce the successful evaluation and constituent aspects of the methodic press to further reflections about the proper application of the test.