Twenty-four patients in a paediatric intensive care unit mostly undergoing cardiac surgery, received a midazolam dosage between 50-400 micrograms/kg per hour as a continuous intravenous infusion partly in combination with fentanyl [0,5-2,5 micrograms/kg per hour] for analgesia and sedation. The mean duration of midazolam infusion was 11.6 days (range 38 h-40 days). Blood samples for the HPLC assay of serum midazolam concentration were taken and the clearance estimated. The efficiency of sedation in correlation to the midazolam concentration was evaluated by a clinical sedation score. Serum midazolam concentrations between 100-400 micrograms/l were sufficient for sedation. Dosage had to be increased during therapy according to an increased midazolam clearance. The evaluation of the sedation score showed that sedation of artificially ventilated infants and young children can be established by continuous intravenous infusion of midazolam.