Abstract
Peroxisomes in Hartmannella culbertsoni were identified by localization techniques for catalase employing diaminobenzidine and hydrogen peroxide at pH 9.0. The peroxisomal reaction required hydrogen peroxide as a substrate and was sensitive to aminotriazole and partially sensitive to cyanide and azide. A strong deposit of reaction product was observed in mitochondria under almost all conditions tested. There appeared to be two enzyme systems in the mitochondria which initiated the oxidation of diaminobenzidine. Peroxisomes were approximately 1 µ in length and were irregular in outline. These organelles possessed a finely granular matrix and were surrounded by a single membrane. Cores and vacuoles were seen in these bodies.