1 The effects of an acute dose (3 mg/kg) of amphetamine on the urinary excretion of phenylethylamine (PEA), p-tyramine, their metabolites, catecholamine metabolites and p-hydroxymandelic acid, a major metabolite of p-octopamine were evaluated in the monkey. Amphetamine excretion was also measured. 2 Amphetamine was slowly eliminated from the body, being found in the urine at least six days after administration. 3 Amphetamine increased the excretion of PEA and decreased that of its major metabolite, phenylacetic acid (PAA). This pattern of changes is similar to that previously found in the urine of chronic schizophrenics. 4 The excretion of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) was markedly reduced, that of vanilmandelic acid (VMA) remained unchanged while 3-methoxy-4-hydroxyphenylglycol (MHPG) was increased on the day of drug administration and persisted for at least a further six days. A similar extended effect on the excretion of p-hydroxymandelic acid (it was reduced) was also observed. 5 The excretion of p-tyramine but not its metabolite, p-hydroxyphenylacetic acid, was decreased by amphetamine during treatment and returned to normal levels six days later. 6 From the results obtained, it was concluded that amphetamine effects on behaviour cannot exclusively be attributed to its influence on catecholamines and that other biogenic amines may be involved. 7 Since PEA elicits many behavioural changes similar to those seen with amphetamine, and since amphetamine increases PEA excretion, we suggest that amphetamine may exert some of its behavioural responses through the release of PEA.