SUMMARYThe effects of the neuroleptanalgesic drug combinations, droperidol 5 mg+phnoperidine 1.5 mg, and droperidol 5 mg+fentanyl 0.1 mg, on the cerebrospinal fluid (c.s.f.) pressure, have been studied in patients with normal c.s.f. pathways during controlled ventilation. The influence of droperidol 5 mg+fentanyl 0.1 mg on intracranial pressure has also been investigated in patients with intracranial space-occupying lesions. In patients with normal c.s.f. pathways, droperidol and phenoperidine produced only small alterations in c.s.f. pressure in either direction, while a significant decrease in overall mean c.s.f. pressure. Similarly, in patients with intracranial space-occupying lesions, droperidol plus fentanyl produced decreases in c.s.f. pressure in all but one of the cases studied. The striking difference between the effect on c.s.f. pressure of these drugs and of the volatile anaesthetic agents could be of importance to the clinical anaesthetist dealing with head injuries or working in a neurosurgical unit, when under conditions of controlled ventilation these drugs could be used as adjuvants to nitrous oxide-oxygen anaesthesia.