A series of ultrahigh-molecular-weight polyethylenes with comparable viscosity-average molecular weights of around 2 x 10(6) has been prepared by using a high-activity Ziegler catalyst at different temperatures (T-poly) in the range 20-90 degrees C, in hexane. The ductility and morphology of the nascent reactor powders have been studied. With decreasing T-poly, the drawability of the reactor powders increased significantly. The morphology of the samples has been characterized by scanning electron microscopy, wide-angle X-ray diffraction and the d.s.c. melting behaviour. On mild etching of the powders with fuming nitric acid at room temperature, more than 1 year was required to obtain fully etched morphologies. The selective removal of amorphous regions was confirmed. Extended fibrils (40-150 nm wide and 1-10 mu m long) connecting globular particles (2-5 mu m in diameter), the amount of which increased with T-poly, were also rapidly etched and disappeared. Both orthorhombic and monoclinic crystals survived even after prolonged treatment (9 months or more). No significant differences in the d.s.c. melting characteristics were observed for the series of reactor powders, which was primarily due to a rapid reorganization during the d.s.c. heating scans. However, the effect of T-poly on the morphology of the reactor powders was reflected in the melting characteristics of the etched samples. Etching proceeded more rapidly for the powders prepared at higher T-poly, although initial crystallinities were comparable for all samples. This suggests that the nature of the amorphous regions depends on T-poly. The crystal thicknesses of the initial powders, evaluated from the melting temperatures of fully etched samples, increased with T-poly These results suggest that polymer segments crystallize near T-poly after having grown longer than a certain length during polymerization. The effect of T-poly on the ductility of the reactor powders is also discussed, based on morphological features revealed by the etching.