lHexagonal LnPO(4) . nH(2)O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) and orthorhombic LnPO(4) . nH(2)O (Ln = Tb, Dy) one-dimensional nanomaterials were prepared through hydrothermal reaction under fine control of the acidity in the mother liquors and with a heating temperature in the range 140-200degreesC. The products were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and infrared spectroscopy. The length and width of the nanowires/nanorods were in the ranges 0.2-5 mum and 10-300 nm, respectively. The phasic and morphological changes of the products due to the acidity of the stock solution and the heating temperature used are also discussed. (C) 2003 Elsevier B.V. All rights reserved.