In white non-inbred male rats interrelations between cross section areas of the thymus structural components have been studied both normal and after medical doses of hydrocortisone injected 1-14 times. The animals' mass and the thymus volume decrease. The changes in the interrelations between cross section areas within the limits of the cortical and medullary substance depend on time of the experiment and during its course are not constant. The total part of the cortical and medullary substance decreases, while a relative area occupied by the supporting structures (interlobular septa) and the blood vessels increases. It depends on the fact that during the first week of the experiment under a progressively developing atrophy in the thymus parenchyma, the blood bed has no time for rearranging. In 14 days of the experiment the part of the blood vessels becomes twice as small. Evidently, it is connected with some reductive processes in the weakly functioning vessels. The thymus rearrangements result in an increasing part of the connective tissue components: the relative part occupied by the interlobular septa increases three times and makes nearly the fourth part of the gland.