SummaryWe investigated the effects of different doses of remifentanil on the end-tidal concentration of sevoflurane required for tracheal intubation in children without the use of neuromuscular blocking drugs. One hundred and thirty paediatric patients, aged 3-8 years, were randomly allocated to receive no remifentanil (group control) or remifentanil 0.1 lg.kgwere anaesthetised using 5% sevoflurane. After loss of eyelash reflex, remifentanil 1 lg.kg )1 was injected over 1 min followed by an appropriate group-dependent infusion and the end-tidal sevoflurane concentration was changed. Predetermined end-tidal sevoflurane concentrations for each group were determined using the Dixon up-and-down method. After the target concentration of sevoflurane was maintained for 5 min, the child's trachea was intubated. Successful intubation was defined as excellent or good intubating conditions. The end-tidal concentration (SD) of sevoflurane for successful tracheal intubation in 50% of children (ED 50 ) were 5.