Summary: Skin sensitivity to pollen extracts has been demonstrated in actively immunized rabbits using trypan blue as an aid, after the method of Ramsdell. The reaction is specific, and is more delicate than the precipitin test as indication of an immune response of the animal. The localization of the trypan blue also occurs in the abdominal fluid of the immune animal following intraperitoneal injection of the pollen antigen. Passive transfer of the skin sensitivity from immune to normal rabbit has been accomplished by the use of large quantities of immune serum.