Communication: A syndiotactic poly(propylene) film (sPP), quenched from the melt at 0 degreesC, was drawn at room temperature up to a draw ratio of lambda = 6. The fibre was analysed under tension by X-ray analysis and FTIR spectroscopy, showing the presence of the oriented crystalline form III described by Chatani, with the chains in transplanar conformation. Then it was unhooked, undergoing a large shrinkage, and reaching a length corresponding to be a draw ratio of lambda = 3.8. X-ray and FTIR analysis showed that in the relaxed fibre, a conformational transition from the trans-planar to the helical form occurred. The relaxed fibre was again submitted to increasing extensions up to lambda = 6, step by step, and the elastic behaviour was analysed through the Mullins' curve and hysteresis cycles. It showed good elastic properties, which appear to be closely correlated to the conformational transition between helical and trans-planar forms. [GRAPHICS] X-ray fibre pattern of sample A6S (after releasing the tension).