A gigantic peroxidase granule was detected in the polymorphonuclear neutrophil leukocytes of the giant salamander, Megalobatrachus japonicus. Among 70 different animals examined, this gigantic peroxidase granule was found only in the giant salamander in apparently healthy condition. This granule was generally localized in the center of the leukocyte, single in number, six to ten μ in diameter, and could be demonstrated both with the ben. zidine peroxidase reagent and the orthophenylenediamine peroxidase reagent. This granule, however, could not be demonstrated with Giemsa stain. It is of interest that one of pathological characters of human leukocytes was found in an apparently healthy giant salamander although it remains to be determined in what way this gigantic peroxidase granule developed only in the neutrophil leukocytes of this animal.
The authors wish to appreciate from their whole heart that Mr. Hiroshi Sugiura, B. S. of the Aquarium in the Uéno Zoological Garden, Tokyo, and Prof. Kiyoshi Hama of the Hiroshima University generously provided the giant salamanders.

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