We describe our evaluation of the Technicon Stat/Ion, an instrument which performs sodium, chloride and bicarbonate analysis simultaneously. 2. All four of the assays resulted in linear response over the entire clinical range with insignificant carryover between specimens. 3. Precision studies for within-run variation were: sodium 0.3 percent, potassium 0.7 percent, chloride 0.5 percent and bicarbonate 1.6 percent. Day-to-day precision was similar to the within-run precision. 4. Comparison methods for sodium, potassium, chloride and bicarbonate utilizing flame photometry, chloridometry and titration of released carbon dioxide respectively showed the following linear regression and correlation coefficients: sodium y=0.96+5.5 (a=0.988) potassium y=1.01x+0.0 (a=.996) chloride y=0.99x+1.0 (a=.993)bicarbonate y=1.0x+1.2 (alpha=.969).