Circadian variation in 5-hydroxyindoleacetic acid levels in human cerebrospinal fluid

Circadian variation of 5-hydroxyindoleacetic acid (5-HIAA) in the ventricular fluid of 5 neurosurgical cases is examined. The 5-HIAA level increases progressively during the day (highest values at 24.00 h) and returns to the initial level the following day at 6.00 h. The results are discussed.