The effect of denervation on the anaphylactic contraction of the diaphragm from actively sensitized guinea pig has been studied. 2. The section of the phrenic nerve took place at cervical and thoracic levels. The sensitization of the animal took place several days before sectioning, simultaneously with denervation and after denervation. 3. The anaphylactic contractions were observed from the fourth day after thoracic denervation, and from the sixth day when denervation was in the cervical region. 4. The hypersensitivity to ACh in the denervated diaphragmatic muscle was present 24 hr after sectioning the phrenic nerve and reached its maximum 3-4 days after. 5. These results support the idea that denervation caused some changes in the membrane of the skeletal muscle fibres to allow the fixation of antibodies. These denervation changes are dependent on the length of the peripheral nerve left to degenerate. Anaphylactic contractions appeared earlier in those animals where phrenic nerve sections were closer to the diaphragmatic muscle.
