Rectal application of methohexital for induction of anaesthesia takes into consideration the child's psychological state. However, quite a lot of side effects may occur that are not dependent on age or body weight but on dosage. A clinical study with 66 children from nine months to seven years of age was performed to find out the most adequate dose of methohexital for rectal application. Three groups of children were given, 20, 25 and 30 mg methohexital/kg BW, respectively. Results obtained suggest 25 mg methohexital/kg BW to be the most adequate dose. Failure of induction was seen in 6%. Side effects like respiratory depression, excitation and unexpectedly high plasma levels of methohexital should be considered possible. Methohexital plasma levels of more than 22 micrograms/ml were obtained. Correlation between the effect and side effects of methohexital on the one hand, and maximal plasma levels on the other, were not seen. Since rectal application of methohexital in fact means induction of anaesthesia it should be given only in the presence of an anaesthesiologist and adequate anaesthesia equipment.