Propofol (2,6-diisoproyl-phenol) is commonly used for anaesthesia and sedation for dental procedures in children and patients with mental disability which limits cooperation (1-3). A previous report suggested that relatively high levels of propofol are required to manage patients with intellectual disabilities (4). In our clinical practice we had noted that patients with autism seem more difficult to manage than patients with other mental disabilities, even under general anaesthesia. We could find little information in the literature for this observation. No studies are available that describe the effects of specific anaesthetic agents for a range of disabilities. Patients with mental disability have been described as needing more sedative agents, yet must still be able to communicate and cooperate with the dental staff (5,6). More hypnotics are required not only for sedation but also for restraint with intellectually impaired patients who are unable to respond to requests during treatment. Our study is, to our knowledge, the first to compare patients with autism and other mental disabilities with regard to their response to the hypnotic effects of general anaesthetics. Since propofol is reported to act via gamma-aminobutyric acid [(GABA).sub.A] receptors (7-10) and autistic patients have a neurodevelopmental disorder that may involve the GABA inhibitory system, including delayed cortical development with larger white matter and lack of the mirror neuron system (11), [GABA.sub.A] receptor sensitivity to propofol in autistic patients may differ from that in other cortically disabled patients. We hypothesised that autistic patients need more propofol to achieve the same level of anaesthesia as other patients. We compared dental treatment cases using propofol for general anaesthesia in patients with autism with those in patients with intellectual impairment not thought to be related to GABA activity in the brain.