The distribution of dopamine D1 and D2 receptor immunoreactivities in the nucleus accumbens and the olfactory tubercle of adult and postnatal male rats were compared with the distribution of tyrosine hydroxylase and dopamine transporter immunoreactivities. An overall co-distribution of D1 and D2 receptor immunoreactivities with tyrosine hydroxylase immunoreactivity was found in the nucleus accumbens and the olfactory tubercle. However, the major finding in this study was, following a more detailed analysis in coronal sections of the shell part of the nucleus accumbens, the existence of nerve cell patches of strong D1 receptor immunoreactivity associated with low D2 receptor, dopamine transporter and tyrosine hydroxylase immunoreactivities. These patches were mainly surrounded by areas of strong D2 receptor, tyrosine hydroxylase and dopamine transporter immunoreactivities and could be found also in the olfactory tubercle. Similar observations were made in postnatal rats. Serial reconstructions of the patches of strong D1 receptor immunoreactivity in the rostrocaudal direction were made. The patches formed a continuous tubular nerve cell system in the shell part of the nucleus accumbens. Since this nerve cell System was found to be surrounded by a high density of dopamine terminals, it may represent a compartment where dopamine transmission mainly acts on D1 receptors via local diffusion (i.e. via volume transmission). However, it must be noted that the D1 receptor rich patches constitute only a small fraction of the nucleus accumbens and the overall density of tyrosine hydroxylase immunoreactive terminals correlates with the density of both D1 and D2 receptors in the nucleus accumbens. In conclusion, the present paper gives new aspects on the chemical microarchitecture of the nucleus accumbens.