The concentration of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), kallikrein-like enzymes and beta-glucuronidase were quantified in the cerebrospinal fluid (CSF) during spontaneous migraine attacks. Plasma levels of kallikrein-like enzymes and beta-glucuronidase, as well as urinary levels of 5-HIAA as free acid and glucuronides were also measured. Correlation of these biochemical findings with various clinical variables showed that 5-HIAA in the CSF did not correlate with either the time sequences of migraine attacks or with clinical division of migraine into classical and common migraine. CSF 5-HIAA correlated positively with HVA, EEG photostimulation, the triggering of food and the therapeutic effect of the so-called antiserotonin treatment, and negatively with esterase activity. Urinary 5-HIAA showed a significant increase during the early headache stage.