Blood lactate monitoring is beneficial to many patients, e.g. critical care patients. However, there are very few non-invasive or continuous monitoring systems for this parameter and significant clinical benefit could be achieved if such systems were readily available. Therefore, the aim of the current study was to investigate the possibility of non-invasively extracting lactate from blood through skin using reverse iontophoresis to monitor blood lactate levels in humans. In vitro reverse iontophoresis studies have indicated that the optimum switching mode for reverse iontophoresis of lactate is continuous direct current but application of current combined with electrode polarity reversal every 15 min was suggested to be used in humans. The reverse iontophoresis technique was applied to 10 healthy volunteers and lactate was successfully extracted through their skin into the methylcellulose gel of the electrodes. A moderate correlation (r<sup>2</sup> = 0.6) between lactate concentrations in collection gels and lactate levels in the blood was observed after an outlier was removed from the regression equation. The result suggests that it may be possible to non-invasively monitor the blood lactate levels using reverse iontophoresis technique.
