In a group of 22 autistic children aged 5 to 16 years and a group of normal controls matched for age and sex, catecholamines metabolism was investigated in plasma, platelets, and urine. This investigation was part of a research project in which several biological parameters (including serotonin) were explored simultaneously in the same children. In the autistic group, epinephrine and norepinephrine were significantly elevated in plasma, while epinephrine, norepinephrine, and dopamine were significantly lower in isolated platelets. No significant difference was found between the two groups for the urinary excretion of epinephrine, norepinephrine, dopamine, DOPAC, and MHPG. Other differences between the two groups in the statistical correlations of several biochemical parameters also suggest abnormalities of bioamine metabolism in the platelets of autistic children.