The development of supersensitivity to dopamine by striatal neurons is widely considered to be a response to interruption of dopaminergic synaptic function. However, it is not clear whether pre-existing dopaminergic innervation is in fact necessary for supersensitivity to develop. In this study, rat foetal striatal cells were obtained prior to their innervation by dopaminergic fibres, and grafted into the cortex or thalamus of adult rats. In the absence of dopaminergic innervation, the grafts developed and became organized into striatum-like and non-striatum-like patches. Both in animals with intrathalamic and in animals with intracortical grafts, systemic administration of a low dose of apomorphine (0.25 mg/kg) induced intense fos expression in striatum-like patches not innervated by dopaminergic fibres. These results indicate that pre-existing dopaminergic innervation is not required for the development of supersensitivity, and that dopaminergic innervation is necessary to develop an adequate synergistic interaction between D1 and D2 receptors.