Pauli writes of a paper by Dürr which contains answers to all questions left open in Heisenberg's letter. He is going to study this paper.

Pauli replies to Heisenberg's letter of 15 March. He emphasizes the discrepancy of their respective views on symmetry diminuation, spatial boundary conditions and rest mass zero . He specifies their differences of opinion. He writes about the logical possibility that electromagnetism and photons cannot be explained by a spinor model.

Pauli gives some more suggestions for formulation of their results.

Pauli writes to Heisenberg about a letter from Laue who thinks that at the "memorial meeting" for Planck one should talk about Planck and not about one's own work.

Pauli writes of his definite decision not to publish together with Heisenberg paper "On the isospin group in the theory of elementary particles", because essential parts of the pre print cannot be backed by him. He says that free to publish the paper alone. He summarizes his own views: 1)out of the degeneracy of the vacuum the possibility of a half-integer difference between ordinary spin and isospin cannot be concluded. 2)The idea of unification of field for strange particles has failed. 3)The eigenvalue problem has not been solved. 4)The physical meaning of the indefinite metric has not been clarified.