SummaryInravenous injection of insulin is followed by a drop in the number of blood eosinophils, in subjects with normal adrenals.This drop is not obtained if glucose is administied with insulin, which shows that the stimulus is hypoglycemia and not insulin itself.The failure to obtain such a drop in 3 subjects with Addison disease and 1 with pituitary insufficiency shows that it is mediated through the pituitary and the adrenal cortex.This method may be useful in the diagnosis of pituitary and adrenal insufficiency.This work confirms the results of Laragh and Almy.