Expression of the serotonin transporter protein (5-NTT) in the dorsal raphe nucleus (DNR) during the early postnatal period was investigated in laboratory Wistar rats. Immunocytochemical labeling showed that during the first 3 postnatal weeks the intensity of 5-NTT expression in DNR of control animals changes. During the earliest postnatal stages, most of DNR subnuclear neurons (dorsal, DNR-d; ventral, DNR-v; lateral, DNR-lat) were found to intensely express 5-NTT. 5-NTT localization sites were revealed on the membrane surface of neuronal cell bodies and their processes in neuropil. On P10, the number of 5-NTT expressing neurons and 5-NTT binding sites decreases. At this time, the 5-NTT binding sites were shown to undergo redistribution becoming very few on neuronal cell bodies and dendrites, but rather densely packed in the axonal membrane. The number of 5-NTT expressing neurons and density of 5-NTT localization sites in neuropil gradually increases with age. The reduction in the serotonin level in all DNR regions during prenatal development leads to the reduction both in the number of 5-NTT expressing neurons and 5-NTT localization sites during the early postnatal period. This tendency was shown to persist with age.