Pauli replies to a letter by Dyson that was dealing with the Källén Formula and general problems of renormalization. He emphazises that not every mathematical solution of the renormalized field theory must have a physical letter from Pauli to Lee gives some remarks to a paper by Lee, especially on the consequences of coupling-constant renormalization and about the occurrance of negative probabilities.

Heisenberg replies to Pauli's question as regards the "Hilbert-space II" formalism, and the commutation relations on the light-cone. He also speculates about the importance of e$^{2}$/h.c.

Pauli sends a list of people to whom preprints of their paper should be sent. He comments the reaction of Heisenberg and his pupils to the paper.

Pauli writes on the non-physical ("pathological") solutions of quantum electrodynamics in case of strict validity of Lorentz-invariance. The mathematical consequences of this: "ghosts" and macroscopic acausalities and the postulate that for large photon- and quantumnumbers of electrons the classical theory must result as limiting case of quantum electrodynamics. One has to look if the equations of quantum electrodynamics have solutions which fulfil these three consequences.