The disturbance of glucocorticoid balance in early postnatal ontogenesis (17-19 days) as a result of prednisolone administration was shown to lead to partial suppression of circadian adrenocortical activity in adult rats. Circadian rhythm of FFA in these groups of animals was undetectable and circadian acrophase of blood glucose concentration changes while diurnal urine periodicity remained unchanged. Diurnal rhythm of locomotor activity in prednisolone-pretreated tars was characterized by later onset of increasing its activity and shorter duration.