Pauli thanks Källén for his reply. He objects to his views on the gauge-invariance. He writes on the danger for a theoretical physicist to stick to one special formalism. This is also Källén's mistake in his formulation of the Lee-model.

Pauli talks about the Schafroth's new paper. He explains why his model gives quantitatively not correct results and how this can be mended. He comments on the papers by Butler and Friedmann. He talks about CERN and about his paper for the

Pauli writes about his contribution to the Bohr Festschrift. He writes about strong and weak reflection, particle and anti-particle conjugation and about biological evolution. He criticises Schwinger's work.

Pauli makes a short reference to Jauch's work.

Pauli replies to Källen's letter and continues the topics in Pauli's last letter. The coupling-free case has to be eliminated from Lee's model because it does not exist in nature.

Pauli sends some information (in the form of questions and answers) on the state of quantum electrodynamics in connection with Fierz's visit to the USA.