SummaryAn automated method for measuring β‐hydroxybutyrate was adapted to the Ciba‐Corning 550 Express™ random access analyzer. The assay was based on a kinetic reaction utilizing hydroxybutyrate‐dehydrogenase. β‐hydroxybutyrate concentration (mmol/L) was calculated ratiometrically using a 1.0 mmol/L standard. Canine serum, plasma, and urine were used without prior deproteinization and only a 30‐μl sample was required. The method demonstrated good linearity between 0 to 2 mmol/L of β‐hydroxybutyrate. Analytical recovery (accuracy) within these concentrations ranged from 85.8 to 113.3%. Both within‐run and day‐to‐day precision were determined, as was specificity of the assay in the presence of a variety of interfering substances. The automated assay was rapid and economical, with reagent stability maintained for at least 2 weeks at 4° C. This assay can readily be applied toward the assessment of ketoacidosis in dogs, and with further v