We determined serum Na+ and Cl- results using Technicon's Flame IV-Auto Analyzer II (FLIV/AAII) system and Kodak's Ektachem 400 clinical analyzer. Our objective was to determine whether Na+ and Cl- results from these analyzers were sufficiently similar to report to clinicians without reference to the system used for the determination. Method precision of the two systems for Na+ results was comparable; whereas Ektachem 400 Cl- results were more imprecise than those determined using the FLIV/AAII, Ektachem Na+ results showed lower correlation with the FLIV/AAII (r = 0.890) and Cl- results were more highly correlated (r = 0.960). When Kodak's newly developed equi-transferant electrolyte reference fluid (ETRF) was used with generation 4 Na+ slides and generation 1 Cl- slides the largest difference observed was 7.0 mmol/L for both Na+ and Cl- results. Using Kodak calibrators and the manufacturer's operational conditions for the Ektachem 400, we observed that a considerable number of sample results for both Na+ and Cl- did not agree within 3.0 mmol/L of the FLIV/AAII values. To corroborate our finding, we also analyzed serum Na+ and Cl- using a Technicon Sequential Multiple Analyzer + Computer (SMAC) system and a Nova 4 + 4 Clinical Analyzer (Nova). We conclude that flame emission systems and direct ion specific electrode systems do not yield comparable Na+ and Cl- results even when total protein and triglyceride concentrations of the samples are within reference ranges.(ABSTRACT TRUNCATED AT 250 WORDS)