The effect of 6-OHDA-induced lesions of neostriatum on locomotor activity, stereotypy and anorexia induced by amphetamine (0.5 mg/kg, 1.5 mg/kg and 5.0 mg/kg IP) was examined. Lesioned rats demonstrated attenuated stereotypy and anorexia but enhanced locomotor activity to amphetamine. Biochemical analysis of dopamine and noradrenaline in specific forebrain areas demonstrated significant dopamine depletion in neostriatum. Dopamine levels in mesolimbic, frontal cortex and hypothalamic areas, and noradrenaline in frontal cortex and hypothalamic areas, were not significantly reduced. The data were interpreted in terms of a response incompatibility hypothesis. It is proposed that stereotyped responses mediated by nigrostriatal dopamine neurones are incompatible with eating. In addition, it is suggested that a second form of competition, at the neuro-anatomical level, occurs between mesolimbic and nigrostriatal systems for motor output pathways and the ultimate expression of behaviour. The role of noradrenaline in amphetamine anorexia is also discussed.