Cholecystokinin (CCK) levels were measured in cerebrospinal fluid (CSF) of patients with adult chronic hydrocephalus syndrome (ACHS) (n = 16) and compared with levels from a control group (n = 11). The CSF concentration of CCK in the ACHS group (0.79 +/- 0.53 fmol/mL) was significantly reduced (p = .002) with respect to the controls (1.55 +/- 0.54 fmol/mL). As CCK-8, the most prevalent from of CCK in the central nervous system, has been demonstrated to play a significant role in several physiological and behavioral actions, the reduced octapeptide values found in ACHS could be involved in the disturbances associated with this disorder. Continuous monitoring of intracranial pressure (ICP) demonstrated different ICP profiles in ACHS. We found that all patients with abnormal ICP records except one showed CCK values under the detection limit. Three of the 4 patients with normal ICP had CCK levels within the normal range. These preliminary studies could evidence that ICP alterations are responsible for part of the loss of brain neuropeptide levels in ACHS.