An extruded film of vinylidene fluoride co monochlorotrifluorothylene (5%) was characterized by X-ray and infrared (40 to 2000 cm(-1)) analysis. On poling the film showed substantial piezoelectric activity (d(31) similar or equal to 20 pc/N and d(32) similar or equal to 2 pc/N) even though the alpha crystalline form of poly vinylidene fluoride predominated. The beta form content measured by the infrared ratio 510/530 cm(-1) increased from 10% to 25% on poling.