Pauli writes about the eigenvalue problem in formal systems without given Hamiltonian and interchange relations (Vertauschungsrelationen), on which, to his opinion, the future of the spinormodel depends.

Pauli cannot agree to Heisenberg's optimism in his letter of 26 March and maintains his criticism expressed in the letter of 25 March.

Pauli writes about his plans for the near future. He critizes the possibility of deriving particles with half-integer regular spin and integer isotopin from a spinor-field.

Pauli writes an appendix to the last letter of the 6 April 1958 and comments on a letter by Symanzik.

Pauli writes a circular letter dissociating himself from the contents of the preprint on the isospin-group in the theory of elementary particles and from his co-author ship with Heisenberg.

Heisenberg expresses his regret at Pauli's letter telling of Pauli's withdrawal from the work. He gives additional comments on the results. He does not want to publish the pre print if Pauli does not appear as co-author.

Pauli sends his timetable for the next two months. He writes about two ways of dealing with the Uhlenbeck-Pais models, and about Glaser's approach.