The performance and suitability for point-of-care use of the Immediate Response Mobile Analyser (IRMA, Diametrics Medical, St Paul, MN) was evaluated in a laboratory setting. An unselected series of patient sample results were compared with results from a Chiron 855 (Bayer, Newbury, Berks. UK) for PO2, PCO2, pH, and ionized calcium, sodium, and potassium. Imprecision and bias were also assessed using aqueous quality control material. Imprecision was unacceptable at all levels for PO2 (lowest CV = 6.1% at a mean of 14.7 kPa) and for 2 of 3 levels for PCO2. The imprecision for the other analytes assessed using this material was <5%. Varying bias was observed for all analytes in aqueous external quality assessment material, sodium having the greatest deviation (mean = −3.5 mmol/L, 95% CI 1.2 mmol/L). For patient samples, the correlation between pH results was poor, although imprecision was acceptable (r2 = 0.814, Sy.x = 0.086). An increasing negative bias was observed with increasing PCO2 concentration, although the correlation was good (r2 = 0.977). A similar association was seen for sodium and potassium, although the correlation between analyzers was not as good (r2 = 0.786 and 0.939, respectively), and the imprecision was also poor (Sy.x = 2.46 and 0.17, respectively). The worst comparisons were observed for PO2 and ionized calcium, with several gross discrepancies between analyzer results for PO2 (r2 = 0.386 and 0.828, respectively, Sy.x = 0.064 and 2.67, respectively). We would not recommend this analyzer for use in a point-of-care setting because of the unreliability of the PO2 results in particular and the difficulties with technique for sample application.