It was investigated the influence of pineal peptides on the aging changes both circadian rhythm of thymic serum factor (FTS) titer in male rats Wistar and circannual rhythms of FTS, the amount of stromal cells-precurcors (CFC-F), granulocyte-macrophage cells-precurcors (CFC-GM), CD4+, Mac-1+ and CD19+-cells in bone marrow of male mice CBA. Epithalamin was injected chronically beginning from 6 month in rats and 4 month in mice. In old animals the rhythmical disturbancers of the indices characterized by loss of fluctuations, displacement of seasonal acrophase, increased or diminished amplitude, inversion of rhythm and desynchronization. After epithalamin injections in rats of 11, 17, 27 months the FTS titer at night increased and in old mice of 23-24 months appeared the peak of hormone level in summer-autumn, restored the difference between the amount of CD4+, Mac-1+-cells in bone marrow in spring and autumn, increased CFC-GM amount in spring, diminished CFC-F in autumn and increased this indice in winter. Epithalon also diminished of CFC-GM and CFC-F amount in old mice in autumn. The retarding age-related disturbances of suprachiasmaticus nucleus of hypothalamus structure, the diminishing corticosterone and testosterone levels at night, the increasing hormones level in summer and the falling in winter plays role in the improvement of thymus and bone marrow rhythmical function in old animals, reseaved epithalamin. The rhythms of most indices rhythms in old animals showed a pattern of adult.