Communication: Films of a commercially available polyarylate (U polymer(R)) containing a photosensitive agent were prepared by means of spin-coating onto copper foil, which showed positive-tone behavior after UV irradiation and development with an ethanolamine/N-methylpyrrolidone/H2O mixture. Scanning electron microscope photographs of the images exhibited fine patterns (approximate to10 mum fine/space resolution) with 9-14 mum film thickness. The pattern-forming mechanism is based on the reaction development patterning (RDP) process, where the main pattern-forming reaction occurs during development.