Abstract: A heat-curable coating composition for cathodic electrocoating which becomes water-thinnable on protonation with an acid contains(A) 50-95% by weight of a polycondensation or polyaddition product having an average molecular weight of from 500 to 20,000 and containing primary and/or secondary hydroxyl groups and primary, secondary and/or tertiary amino groups, and(B) 5-50% by weight of a crosslinking agent obtainable by reactinga) an aliphatic polyhydroxy compound andb) an aromatic polyhydroxy compound withc) an aliphatic and/or cycloaliphatic polyisocyanate andd) a blocking agent.