The effect of dexamphetamine (DEX) on striatal multi-unit activity was examined in freely moving rats and again 24 or 48 hr later during immobilization. Animals which in the freely moving state responded with striatal activation following DEX, 1 mg/kg IP, did not respond to this dose of DEX after immobilization. Similarly with DEX 2.5 mg/kg IP, the incidence of excitatory responses seen in freely moving animals decreased to 18% after immobilization, and the incidence of inhibition and biphasic responses increased from 0% in freely moving animals to 52% in immobilized preparations. The results suggest that the response of striatal neurons to DEX is dependent upon the behavioural state of the animal. Furthermore, these findings indicate that the central actions of DEX are more complex than previously believed, and raises the speculation that the excitatory effects of DEX on striatal neurons may be mediated through excitatory striatal afferents.