β-Endorphin (β-EP) and cholecystokinin 8 (CCK-8) concentrations in peripheral blood mononuclear cells were measured in 12 drug-free autistic (AU) children, in 10 drug-free children with pervasive developmental disorders (PDD) and in 11 healthy controls. The aim of the study was to see whether or not there was an alteration of β-EP and CCK-8 concentrations in this peripheral compartment, in which it has been suggested that secretion and regulation of the two peptides mimic those of neurons in the central nervous system. Mean β-EP values were significantly higher in AU than in PDD and control children, while there were no differences in CCK-8 values of the three gro