Background: The dorsal raphe nucleus (DRN) is one of the main serotonergic nuclei in the mammalian nervous system which is involved in many functions. The DRN mainly consists of the largest number of serotonergic neurons intermingled with catecholamine containing neurons. In order to define the morphology and location of tyrosine hydroxylase immunoreactive (TH-ir) cells in different areasof DRN we performed TH immunohistochemistry for the adult rat DRN.Material & Methods: Adult Sprague-Dawley male rats (250-300gr) were used in this study. Following transcardially perfusion-fixation with aldehyde solutions, the brain stems were removed. By using vibrotome, 40mM thick coronal sections were cut and then processed for TH immunohistochemistry. Sections were mounted and cover slipped and studied by light microscopy.Results: TH positive neurons were observed mainly in the rostral up to the end of the central part of DRN. Four types of TH-ir neurons with different distribution were observed in the nucleus. Among the total counted cells, the ovoid and polygonal neurons respectively showed the highest and lowest density in DRN.Discussion: The TH positive neurons in DRN that could be dopaminergic in nature may participate in their major projections to the different areas received putative dopaminergic inputs from DRN, i.e. the striatum, hippocampus and the basal forebrain. None of the serotonergic projections from DRN influence the functions of these areas.