Abstract
A single injection of chlorpromazine (10 mg/kg) caused a large drop in eosinophiles, leucocytes and platelets in the blood and in the mast cells of the mesentery. The effect of this drug on mast cells is negligible in cold acclimatized animals. This is associated with the smaller hypothermic effect of chlorpromazine in acclimatized animals than control animals. The effect of chlorpromazine on formed elements of the blood and mast cells in the rat is not a direct result of hypothermia.