Barbiturates retain an important place in clinical neurological practice. They are used as both diagnostic and therapeutic drugs, their most common uses being as anticonvulsant and anaesthetic agents. This article explores the current theories explaining the mechanism of action of the barbiturates, with special emphasis on their anaesthetic and anticonvulsant effects. The primary mechanism of action of barbiturates is to increase inhibition through the gamma-aminobutyric acid (GABA) system. Anaesthetic barbiturates also decrease excitation via a decrease in calcium conductance. Phenobarbital (phenobarbitone), the primary anticonvulsant barbiturate, is effective for partial, complex partial and secondarily generalised seizures. While no longer the drug of choice for all these seizure types, it remains an important and useful agent. Mysoline has been shown to be useful in the treatment of essential tremor and several other movement disorders, and as an anticonvulsant. Barbiturates are also used for their sedative-hypnotic properties. A relatively new use is in the evaluation of patients with medically intractable seizure disorders for possible surgical therapy. The roles of methohexital and amobarbital (amylobarbitone) are discussed in the section on barbiturates used as diagnostic agents. The experimental use of barbiturates is also commented on; the most important of these is perhaps the use of barbiturates in cerebral resuscitation.