Many metallic implants used in orthopaedics are made of stainless steel or cobalt-chromium alloys which contain 18-30% chromium. Hexavalent chromium has been shown to be the predominant form of chromium released following in vivo and in vitro corrosion of these metal implants (Merritt & Brown, 1995). Blood chromium levels may be elevated between 50 and 250 times in patients with metal hip implants (Lhotka et al., 2003). At physiological pH, hexavalent chromium exists predominantly as the chromate anion and as such can enter cells via non-specific anion channels. The anionic hexavalent chromium diffuses readily through the red blood cell (RBC) membrane and is bound by the haemoglobin probably after its rapid reduction to the cationic trivalent state within the RBC (Gray & Sterling, 1950). The aims of this study were; i. To investigate the effect of the presence of chromium in RBCs on oxygen uptake [Oxyhaemoglobin saturation (O₂-SAT) at specific pO₂ values] ii. To evaluate the suitability of the two commonly used anti-coagulants, heparin and EDTA, for oxygen uptake studies. Blood stabilized by either EDTA or sodium heparin was spiked with clinically relevant concentrations of hexavalent chromium ranging from 0-40µg/L. The spiked blood was equilibrated with two different gas mixtures (2.5% O₂; 5% CO₂; balance N₂ and 5% O₂; 5% CO₂; balance N₂) for 20 minutes. The pH, pO₂, pCO₂ and O₂-SAT were measured using an aliquot of the blood after equilibration. A single factor analysis of variance (ANOVA) showed no significant difference (p>0.05) between experimental O₂-SAT values in the presence and absence of hexavalent chromium in blood stabilized by either anticoagulant. No significant difference was observed between the experimental O₂-SAT values in heparinised blood and O₂-SAT values predicted from standard oxygen dissociation curve nomograms at the same pO₂ and acid-base status. In contrast, the experimental values using EDTA treated blood were significantly higher than the theoretically expected values (p<0.05). This shows that: i. The presence of chromium in RBCs does not significantly affect the oxygen uptake capacity of haemoglobin. ii. Heparin is a more suitable anticoagulant for blood pH and blood gas analysis than EDTA. This is probably due to the ability of the latter to chelate metal ions like Ca²⁺ and interfere with blood chemistry by decreasing the CO₂ combining power of blood.