We evaluated the analytical performance of 10 representative channels on the new microprocessor-controlled DuPont aca III according to the guidelines (draft documents PSEP-2, 3, and 4) proposed by the Instrument Evaluation Subcommittee of the National Committee for Clinical Laboratory Standards. These guidelines were used for the experimental design and data analysis for the precision and accuracy testing, the latter by comparison with an aca II, with results of atomic absorption spectroscopy for calcium, and with the National Glucose Reference Method. From a 20-day replication study, we estimated within-run, between-run/within-day, between-run/between-day, and total standard deviations at three concentrations for each method. From duplicate analyses of 100 samples on the aca III, aca II, and other methods, we estimated the bias from the regression line at specific concentrations and total error from a tolerance limit about the regression line. Analytical performance of the aca III was judged acceptable because these estimated errors were small.