To determine the plasma and cerebrospinal fluid (CSF) levels of urapidil after i.v. administration and the effect on CSF serotonin and 5-hydroxyindoleacetic acid (5-HIAA) concentrations.Open, single-dose study.Post-surgery following neurosurgical removal of the hypophysis (n = 5) or aneurysm clipping (n = 1).6 patients, aged 32-71 years, with intact blood-brain barrier (BBB); 1 patient was studied twice.Single dose of 25 mg urapidil i.v. as prophylaxis of BP increase during extubation or as treatment of hypertensive episodes.Urapidil, serotonin and 5-HIAA were measured by HPLC in CSF during 8 h after urapidil administration. Urapidil was detected in CSF as soon as 5 min after injection in 3 patients. The concentration ratio of plasma/CSF after the distribution phase was about 5:1. No significant effect on serotonin and 5-HIAA in CSF was seen.After administration of a therapeutic dose, urapidil permeates the BBB and may interact with central 5-HT1A-receptors.