We compared haemoglobin concentration values obtained using a portable haemoglobinometer, the HemoCue, in the operating theatre with the results obtained by the Coulter Max-M in the laboratory. Haemoglobin concentrations were measured on 52 arterial blood samples obtained from 13 patients during aortic surgery, in theatre with the HemoCue and again by the Coulter Max-M. Twenty routine samples from the laboratory were also analysed by both methods. There was no significant difference between results, with a mean of 10.94 g.dl−1 and 10.90 g.dl−1 for the HemoCue and Coulter, respectively (p = 0.12, t = −1.99, df = 70). The limits of agreement of the two methods (mean difference ± 2 SD) were −0.37 and +0.45 g.dl−1. The coefficients of repeatability of the 20 samples analysed in duplicate on each device were 0.26 g.dl−1 and 0.33 g.dl−1, respectively. The coefficients of variance were 0.74% (HemoCue) and 0.93% (Coulter). With adequate training and monitoring, the HemoCue provides comparable haemoglobin results for near-patient testing in theatre.