The clearance rate of Cr⁵¹ labelled S. gallinarum endotoxin from the circulation of the hen was investigated. The relationship between the dose of endotoxin and the disappearance rate or radioactivity from the blood was observed. It was noted that radioactivity in the blood deoreased faster after injection of 5 mg of endotoxin than after administration of 10 mg. These differences were most pronounced during the first hour of observation and diminished later. Blood radioactivity of Cr⁵¹Cl₃ was disappearing slower than that of labelled endotoxin.