At present the diagnostic method NMR (Nuclear Magnetic Resonance) is very popular and useful, mainly in medicine. It is based on the principle of free (Lamor) precession or free induction called FID (Free Induction Decay). Free precession was used in the method called “spin echo” which was known many years before the tomographs were constructed in their current form. In principle the method “spin echo” uses radiation of a sample (organic material) by pulses of high frequency electromagnetic radiation (pulse NMR) and measures relaxation time of protons present in the test sample. Relaxation times are typical processes for the exchange of energy between the sample and its environment. The author of this article used this method and carried out the measurements with his colleagues from the Faculty of Sciences, Comenius University in Bratislava, already in 1960s. In the paper the author describes some basic experiments carried out by means of “spin echo” method and he also presents their interpretation.