Summary: The quantitative relations in partial desensitization are contrasted with those that obtain in the state of lessened sensitiveness in allergy, the differences being such as to indicate a difference in the mechanism of these two phenomena. The phenomenon of “local exhaustion” of the allergic cutaneous reaction described by Mackenzie and Baldwin is studied and found, in disagreement with these authors, to be non-specific. It is proposed to distinguish the lessened sensitiveness induced in allergy from the state of desensitization in anaphylaxis by designating the former condition as a state of hyposensitization.