Background: The role of thyroid hormone (TH) disbalance in genesis of psychological disturbances in the adult humans is well known. A phenomenon of 'central thyroid hormone homeostasis' characterized by increased synaptosomal T3 content, deiodinase type II (DII) activity and cAMP level, is known to exist during peripheral hypothyroidism. This phenomenon tries to counteract the adverse psychobehavioural manifestations commonly associated with TH deficiency. A close physiological association between sympathetic nervous system activity and TH is well known. Dopamine, a predominant catecholamine neurotransmitter in the mammalian brain, controls a variety of functions including locomotion, cognition, emotion and also affects neuroendocrine secretion. In the present study relationship between TH and dopamine has been presumed to be involved in the maintenance of 'central thyroid hormone homeostasis' in adult rat.