An intensification of a swimming behavior with an increase in the proportion of active swimming and limitation of the duration of immobilization was found in rats following bilateral electrolytic destruction of the suprachiasmatic nuclei of the hypothalamus. The restructuring of the temporal dynamics of swimming is manifested in a limitation of the rhythmological index of depressivity. The animals with ablated nuclei demonstrate more pronounced behavioral disturbances in response to the introduction of fenamin and a slowing of the minute fluctuations in the dynamics of stereotypic behavior.