Thermoplastic polyamide resins showing improved substrate adhesion and consisting essentially of polycondensates of the following components:(a) from 10 to 50 mole percent dimer fatty acids, having a trimer fatty acid content of from 10 to 20 mol percent;(b) from 25 to 45 mole percent of one or more aliphatic, aromatic and/or cyclic C.sub.2 -C.sub.40 diamines which are diprimary diamines, diamines containing secondary amino groups and alkyl substituents with no more than 8 carbon atoms on the N-atom, or heterocyclic diamines capable of diamide formation,(c) from 5 to 25 mole percent of aliphatic diamines capable of diamide formation and N-alkyl-substituted on at least one N-atom, containing from 2 to 10 C-atoms and from 10 to 25 carbon atoms in the N-alkyl group, and(d) from 0 to 40 mole percent aliphatic C.sub.6 -C.sub.22 dicarboxylic acids.