Urinary catecholamines (DA, NE, E) and their main metabolites (HVA, DOPAC, MHPG) were analyzed both as free and conjugates in eight children diagnosed as autistic according to DSM-III criteria and eight normal children. Significant differences appeared for the urinary excretion of both DA and NE and their respective metabolites: Autistic children showed low DA, high HVA, high NE, low MHPG urinary levels. These results are consistent with previous findings on altered catecholamine metabolism in autistic children. They suggest that autistic behaviors might be related to an abnormal functional imbalance among monoamines either at a molecular level or at a system level. Furthermore, they emphasize the special interest of urinary assays in pediatric research.