The purpose of this investigation was to assess the reliability of the i-STAT clinical portable analyser and CG 4 + cartridge measures of blood pH, partial pressures of O 2 (pO 2 ) and CO 2 (pCO 2 ), bicarbonate ([HCO 3 − ]), base excess (BE), total carbon dioxide (TCO 2 ), oxygen saturation (sO 2 ) and blood lactate ([BLa − ]) at various exercise intensities. A comparison between [BLa − ] measured by the i-STAT and the Accusport lactate analysers during an intermittent treadmill run was also undertaken. The technical error of measurement (TEM%) at rest, at moderate (200W) and maximal exercise (V˙O2 max) was acceptable (<15%) for all parameters. The intra-class correlation coefficients for each analyte ranged from weak-to-strong across resting (ICC=0.19–0.96) and moderate (ICC=0.30–0.96) exercise intensities. The ICC for all analytes were observed to be strong following maximal intensity exercise (ICC=0.77–0.95). The comparison of the [BLa − ] measures between the i-STAT and Accusport showed that the difference between measures was acceptable at both low (<4mmolL −1 ) (−0.39±0.27mmolL −1 ), moderate to high concentrations (>4mmolL −1 ) (0.58±1.22mmolL −1 ), and across all [BLa − ] data (0.36±1.13mmolL −1 ). In conclusion, the i-STAT clinical analyser and CG 4 + cartridge provides reliable measures of a number of blood parameters across exercise intensities. The [BLa − ] measures from the i-STAT analyser are consistent with that of the Accusport lactate analyser.