This report addresses the effects of chronic blockade of D₂ receptors with haloperidol on the behavior of rats with low levels of depression. Chronic blockade of D₂ receptors with haloperidol (2.5 mg/kg) had a phasic prodepressant action on the behavior of rats with a low basal level of depressivity and led to the formation of a depressive state. The index of depressivity in control and experimental animals showed weekly and half-weekly rhythms characterized by phase shifts relative to each other.