In each of the legal proceedings, in which expert evidence is carried out, a major concern is the assessment of the evidential value of expertise. Judicial institutions, while making decisions, rely heavily on the expertises, because they usually do not possess 'special knowledge' from a certain fields of science. Expert’s opinion is therefore an important evidence in the case, i.a. on this basis, judicial institutions make their decisions. It can have farreaching consequences for the parties of the trial. Within each expert report, expert applies a chosen method, which enables the answer to the questions raised by the judicial institution. However, methods used within various forensic sciences are characterized by a varying degree of intersubjectivity. Experts dispose relatively great freedom during the process of trace analysis, which often results in differences in the shaping of the conclusion. Recent studies indicate a number of factors that are responsible for this undesirable situation. One of them may be too low rank of law regulations, harmonizing the methods used by forensic experts in various fields. In many branches of forensic sciences, specific methods or standards of working there are still not developed and there is lack of legal regulations relating to this matter. From the point of view of legal authorities, whose task is to assess the probative value of the expertise, it is an important practical problem. These authorities are not able to check or trace the way of the expert's proceedings.

Keywords: Research methodology, verification of sciences methods, reliability of methods, intersubjectivity of forensic sciences methods.