An acute dose of D-amphetamine (5 mg/kg) caused marked stereotyped licking, sniffing and gnawing, and hyperactivity. These effects were prevented by chlorpromazine. DOPAC and HVA were assessed in 4 brain areas (striatum, amygdaloid cortex, olfactory lobes and brain stem) following the administration of these drugs. It was found that the amphetamine-induced changes in dopamine metabolism in both the striatum and olfactory lobes returned to control levels following chlorpromazine treatment. It is suggested that the behavioural changes induced by amphetamine are a consequence of changes in dopamine metabolism in both the striatum and mesolimbic systems. The acute administration of amphetamine also caused an increase in the concentration of tryptophan and 5-HT in the brain stem, striatum and some regions of the limbic system. Chlorpromazine also raised the concentrations of these substances when given alone but in combination with ampheeamine reduced the concentration of 5-HT to control values in the striatum, olfactory lobes and amygdaloid cortex but raised it in the brain stem. Thus 5-HT may play an ancillary role in amphetamine induced behavioural changes.