Internally blocked polyurethane curing agents for ecological powder lacquers were synthesized by the Bu(2)Sn dilaurate and Et(2)N-catalyzed reaction of 1.6-hexamethylene, trimethyl-1,6-hexamethylene, isophorone or 4,4'-dicyclohexylomethane diisocyanates either with BuOH and blocking agents (imidazole, 3,5-dimethylpyrazole, e-caprolactam) at 130-150 degrees C to produce the allophanate bonds or with HCOOH and the blocking agents at 140 degrees C to produce the biuret bonds. The curing agents were characterized by IR, (1)H-NMR and (13)C-NMR spectroscopy as well as by gel permeation chromatog. and used for prepn. of powder lacquers by compounding with the Rucote-102 polyester resin and curing at 150-200 degrees C for 30-50 min. The lacquers (layer thickness 60-152 mu M) showed good impact resistance, adhesion to the glass and steel substrates, cupping, elasticity and gloss.