Pauli comments on a letter by Källén and his problem of two N-particles.

Pauli talks more about the indefinite metric which Pauli rejects.

Addendum to appendix of last letter, giving Pauli' conclusion. The discussion with Heisenberg has not brought him nearer to a possibility of interpreting physically the formulae derived from the indefinite metric.

Pauli suggests suspending the discussion until new points of view emerge.

Pauli is pleased whith Heisenberg's letter of 24 February and continues the discussion.

Pauli replies to Heisenberg's letter of the 30 October, on $\gamma$-invariance and conservation of electric charge: which group corresponds to this? He talks about mirror-invariance in isotopic spin space.

This is the continuation of the letter of the 16 January 1958. Pauli gives a new idea of indefinite metric.

Pauli acknowledges receipt of Heisenberg's manuscript and makes a few comments.

Pauli discusses "Part IV" of Heisenberg's S-matrix theory published in: Zeitschrift für Naturforschung: 1, 608.

Pauli thanks Hulthén for sending the French edition of Lagervist's work on the Lamb shift.