Objective To study the distribution of DARPP-32 in the rat brain. BR>Methods Immunohistochemical staining techniques were applied to study the localization of DARPP-32 in neurons of the rat brain. Results The strong immunoreactivity for DARPP-32 was localized primarily in the basal ganglia and the anterior olfactory area, involving neuronal cell bodies or dendrites in the nucleus accumbens, caudate putamen, amygdaloid nucleus and fibers throughout the globus pallidus, ventral pallidum and pars reticulate of the substantia nigra. The moderate to weak immunoractivity for DARPP-32 was observed in red nucleus, septofimbrial nucleus, purkinje cells in cerebellum, medial habenula nucleus, cortex and hippocampus. DARPP-32 was present in the cytoplasm, cytomembrane and cell nucleus of labeled neuronal somata and dendrites. Conclusion DARPP-32 is widely distributed in the rat brain. It is primarily present in the neurons, which receive a dopamine input and contain dense of the D1 receptor. DARPP-32 may play an important role in dopaminoceptive neurons. BR>