Films of Re0.25Ba2Ca2Cu3Ox precursors have been produced in-situ by spray pyrolysis as a preliminary step of the synthesis of Hg-based superconductor films without post-annealing treatment. The films are homogeneous with smooth surfaces. The films are a mixture of BaCuO2, Ba4Ca1+xRe2-yO12, CuO and CaO that transform to Ca2CuO3 only after post-annealing. These phases are found to be strongly textured with respect to the underlying single-crystal substrates (LaAlO3 (001) and MgO (001)). The CuO does not grow with the same orientation on LaAlO3 and MgO. After ex-situ mercuration, Hg-1212 on LaAiO(3) and Hg-1223 on MgO are formed epitaxially thanks to a CuO buffer layer. (C) 2004 Elsevier B.V. All rights reserved.