Cerebrospinal fluid (CSF) concentrations of neurotensin (NT) and corticotropin-releasing hormone (CRF)-like immunoreactive materials (LIM) were measured in 22 infants and children 6 days to 15 years of age. For both neuropeptides there was a marked age-related exponential decline in CSF concentrations. The most prominent decrease in CSF neuropeptide concentrations was seen during the first 24 months of postnatal life. From 1 year and on there was no or only minimal age-associated alteration in CSF neuropeptide concentrations. In this group of children (1-15 years) mean CSF concentrations of NT-LIM and CRF-LIM were 36.8 +/- 4.32 and 65.9 +/- 4.63 pg/ml, respectively. As CSF neuropeptide concentrations are apparently independent of circulating serum concentrations, they may reflect functional activity of neuropeptide-containing neurons and therefore may be of value in the assessment of the role of peptides in the human central nervous system function and behavior.