This paper presents an elementary derivation of formulas for the spin·relaxation parameters. The derivation is based on the solution of the equation of motion for time correlation functions of the magnetization. The use of the assumption of regression of fluctuations allows the determination of non linear integral equations for the relaxation para­ meters. The method leads to the conclusion that the information obtained through Magnetic Resonance experiments is totally contained in two time Green's functions of the magnetization components.