A postal survey was conducted to determine how thiopental is used in UK neurosurgery critical care units. Thirty units were contacted and 26 replied. Thiopental is used in 23 units. The majority (60%) of these units govern the use of thiopental with protocols or guidelines and 74% use cerebral monitoring to guide dosage. When patients have had thiopental, 20 units delay brain stem testing, two will not perform tests and one unit incorporates cerebral angiography into their protocol. Twelve units use serum thiopental assays in their brain stem testing procedures, but there is wide variation in the interpretation of the results. We found inconsistency and confusion surrounding brain stem testing in this patient group, raising the possibility of misdiagnosis of brain stem death.