Dopamine exerts a tonic inhibitory control in the regulation of mRNA encoding preproenkephalin (PPE), the precursor of enkephalin, in the dorsal part of the rat striatum. Less is known about the role of this amine in the regulation of PPE mRNA in the ventral part of the striatum which corresponds to the nucleus accumbens. In this study, the effects of an interruption of dopamine transmission by haloperidol (a dopaminergic receptor antagonist) were examined in the rat nucleus accumbens. The levels of PPE mRNA were analysed by in situ hybridization histochemistry by taking into account the complexity of the nucleus accumbens, i.e. by differentiating the rostro-caudal extension of the structure. It was found that PPE mRNA content was increased significantly only in the caudal part of the nucleus, indicating rostro-caudal differences in the haloperidol effects. The differential reactivity of PPE mRNA to dopaminergic receptor blockade and to a lesion of dopaminergic neurones along the rostrocaudal axis of the ventral striatum is discussed.