Failure of dental treatment due to anxiety is a common problem in children. The aim of this study was to establish whether the use of a combination of intravenous midazolam with inhalation agents (nitrous oxide alone or in combination with sevoflurane) was any more likely to result in successful completion of treatment than midazolam alone. A further aim was to evaluate the clinical viability of these techniques as an alternative to general anaesthesia. In total, 697 children too anxious for management with relative analgesia and requiring invasive dental procedure for which a general anaesthetic would usually be required, were recruited and randomly assigned to one of three groups given the following interventions: group 1 - a combination of inhaled medical air and titrated intravenous midazolam, group 2 - a combination of inhaled 40% nitrous oxide in oxygen and titrated intravenous midazolam, and group 3 - a combination of an inhaled mixture of sevoflurane 0.3% and nitrous oxide 40% in oxygen with titrated intravenous midazolam. The primary outcome measure was successful completion of the intended dental treatment with a co-operative child responsive to verbal commands. In group 1, 54% (94/174 children) successfully completed treatment. In group 2, 80% (204/256 children) and in group 3, 93% (249/267 children) completed treatment. This difference was significant at the 1% level. Intravenous midazolam, especially in combination with inhaled nitrous oxide or sevoflurane and nitrous oxide, are effective techniques, with the combination of midazolam and sevoflurane the one most likely to result in successful treatment.