Cathodically depositable, aqueous coating compositions comprising the reaction product of (A) diene polymers containing free hydroxyl groups with a hydroxyl number of at least 40 mg KOH/g and an average maximum molecular weight of 4000; and (B) a compound having an average of from about 0.8 to 1.5 free isocyanate groups and at least one basic aliphatically bound nitrogen atom. Optionally, there can be included in the reaction product a compound having from about 0.8 to 1.5 free isocyanate groups and from 1 to 3 ethylenically unsaturated double bonds. The coating compositions cure at relatively low temperatures and relatively short curing times to provide films having excellent resistance to water, chemicals, and corrosion.