Objective - complex assessment of morphological changes in the adrenal medulla (AM) after partial laser destruction of a paired organ, based on the calculation of variation coefficients and the identification of natural periods Material and methods. On sections of the adrenal glands of adult rats (n=41), with a differentiating staining of adrenalocytes and noradrenalocytes, morphometry of 19 AM parameters was performed during 2 months after a surgical laser injury to the paired organ. The data were processed according to the natural periodization method. Results. According to the degree of variation of the parameters in each time point from their average values for the entire observation period and from control we calculated the coefficients of variation Cv and Cvc. Their dynamics allowed us to reveal the natural periods: I period - enhanced response (1-14 days) with phases I.1 - a quick, but weaker reaction (days 1-7) and I.2 - a slow, but stronger reaction (7-14 days); and II period - normalization (days 14-56). Passing the curves of Cvc and Cv through the time point of the 21st day almost in a straight-line indicates a possibility of optimizing similar experiments taking into account this time point. The convergence of all parameters with the control on the 56th day shows that it is impractical to prolong the experiment. Conclusions. 1) The crucial point of the systemic reaction of AM as a paired structure to laser damage is the 14th day. 2) When planning similar experiments, it is possible to optimize them taking into account the 21st day. 3) Extension of similar experiments longer than 2 months is not rational.