OBJECTIVES: We aimed to document our experience with oral clonidine when used as a sedative in combination with intravenous morphine and lorazepam in a group of mechanically ventilated children with single-organ, respiratory failure. In particular, our objectives were to establish the relationship between oral dose, plasma concentration, and sedative effect, and second, to document the side-effect profile. DESIGN: Prospective, cohort study over a 72-h period. SETTING: Regional paediatric intensive care unit. PATIENTS AND PARTICIPANTS: Twenty-four children were enrolled (median age 3 months) of whom ten were excluded (six due to extubation before 72 h, three sedation failures, one protocol violation). MEASUREMENTS AND RESULTS: Plasma clonidine was measured using gas chromatography mass spectrometry, and sedation assessed using the COMFORT score. Using a dose of 3-5 microg/kg every 8 h, plasma concentrations appeared to plateau at approximately 41 h giving a mean value of 1.38 ng/ml (95% confidence interval 1.0-1.8). Adequate sedation was achieved during 82% (837/1022 h) of the study period; however, this decreased to 70.3% when analysed on an intention-to-treat basis. There was a concomitant overall decrease in the average hourly requirements for both morphine ( P = 0.02) and lorazepam ( P = 0.003). There were no documented episodes of bradycardia, hypotension or hyperglycaemia. CONCLUSIONS: Oral clonidine may be a safe and effective sedative in combination with morphine and lorazepam for young children with single-organ, respiratory failure. This agent may also exhibit opioid and benzodiazepine sparing effects in this patient group. A full pharmacokinetic study is warranted.