Abstract: The present invention provides a process for preparing a trisubstituted urea of the general formula:R(NHCONR'R").sub.nin which R is a substituted or unsubstituted mono-, di- or polyvalent aromatic radical, R' is a substituted or unsubstituted monovalent aliphatic or aromatic radical and R" is a substituted or unsubstituted monovalent aliphatic radical or R' and R" together represent a substituted or unsubstituted divalent radical in which at least one of the two carbon atoms adjoining the nitrogen atom of the urea is aliphatic, and n is an integer, wherein an aromatic nitrocompound of the general formula:--R(NO.sub.2).sub.n or an aromatic nitrosocompound of the general formula:--R(NO).sub.n is allowed to react with a secondary ammonium N,N-disubstituted thiolcarbamate of the general formula:R'R"NCOS.sup.-.NH.sub.2.sup.