Abstract: Diphenylamine-formaldehyde containing N,N,N',N'-tetraphenyldiaminomethane as the principal product of reaction is obtained by:(1) In a first stage, heating together a mixture of diphenylamine and formaldehyde in a molecular ratio of from 3:1 to 1:1.5 at a temperature of up to 110.degree. C. until evolution of water is substantially complete, then in a second stage,(2) heating the resultant mixture at a temperature of from 120.degree. C. to a maximum of 140.degree. C. with exclusion of oxygen or oxidizing agents, and removing water and formaldehyde from the reaction mixture until the proportion of bis-(N,N-diphenylaminomethyl)ether present in the mixture falls to below 10% by weight.The molten reaction product is preferably converted to a solid product by pouring into a stirred, relatively cool immiscible liquid, and coating the resulting granules with a small amount of magnesium oxide or magnesium carbonate.