Rat brain polymorphonuclear infiltration was quantitated by spectrophotometric assay of myeloperoxidase activity. Peroxidase was assayed by following the oxidation of o-dianisidine in the presence of a hydrogen peroxide generating system (glucose-glucose oxidase). Enzyme activity was proportional to the number of polymorphonuclear leukocytes present at densities between 105 and 106 cells. Brain tissue did not have detectable peroxidase activity and polymorphonuclear leukocytes added to brain

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... ogenates were quantitatively estimated. In infant rats with Haemophilus influenzae meningitis, the correlation between the number of polymorphonuclear leukocytes found in brain by peroxidase activity measurement and independent histological grading was not precise, but there was an exact correlation in predicting presence or absence of polymorphonuclear leukocytes. Myeloperoxidase activity appears to afford a rapid convenient tool for quantitative determination of tissue polymorphonuclear leukocyte content.