The duration of sensitization in guinea pig injected with antiegg white rabbit serum was measured by the passive anaphylaxic method. The results were as follows, 1. The precipitin of the passive sensitized guinea pig remained in its blood vessel in proportion to sensitized precipitin titer. 2. The duration of sensitization measured by foetal anaphylaxis took a longer time in proportion to sensitized antibody titer. 3. It was found that the complement titer after anaphylaxis proved decrease in proportion to the sensitized precipitin titer.