SummaryWe report laboratory and clinical evaluations of a blood propofol concentration analyser. Laboratory experiments used volunteer blood spiked with known propofol concentrations over the clinically relevant concentrations from 0.5 to 16 lg.ml )1 to assess linearity and the influence of haematocrit and concurrent drug administration. Analyser concentrations demonstrated excellent linearity (R 2 = 0.999). Blood spiked with commonly used drugs showed no significant variation compared to unspiked controls. Propofol measurements were largely independent of haemoglobin concentration. A 6% decay in propofol concentration was observed at the highest prepared concentration. Clinical performance of the analyser was assessed using 80 arterial blood samples from 72 patients receiving propofol infusions during cardiac surgery. Samples were processed using the propofol analyser, and high performance liquid chromatography (HPLC) used as a gold-standard comparator. These data demonstrated excellent agreement between the propofol analyser and HPLC with a bias of 0.13 lg.ml )1 and precision of )0.16 to 0.42 lg.ml Target-controlled infusion (TCI) is a common method of propofol administration. The ability of TCI algorithms to predict blood propofol concentrations accurately is poor [1, 2], with measures of precision demonstrating errors of up to 60% [3]. Significant bias and large errors in precision are also identified in groups falling outside of limits used in the development of these algorithms [4][5][6]. Conventional methods of measuring propofol concentrations in blood include high performance liquid chromatography (HPLC), gas chromatography and liquid chromatography mass spectroscopy. These are labour intensive and time consuming methods and cannot be used to deliver clinically useful information. Estimation of blood propofol from expired gases has yet to demonstrate consistent and reliable results [7].We assessed a device designed to measure the concentration of propofol in a blood sample in 4 min by extracting propofol from 0.5 ml of whole blood using solid phase extraction and quantifying the amount of propofol in the extract using colorimetric detection techniques. This technique for propofol extraction was first described in 2006 in a proof of concept study [8]. We conducted both laboratory and clinical evaluations of the device, the latter using samples from patients undergoing propofol-based general anaesthesia for cardiac surgery.