Thirty-one children with autistic disorder, 8 with the Rett syndrome (RS), 2 with childhood disintegrative disorder and 5 with infantile spasms were compared with healthy adult controls with respect to cerebrospinal fluid (CSF) beta-endorphin levels. The autistic disorder and RS groups showed significantly lower values than the other groups. There were no age trends within the various groups. Further study of CSF beta-endorphins in these disorders and blindly examined age matched controls is warranted.