The incorporation of cobalt ions from various CoCl2 solutions into polyaniline (PANI) has been investigated. PANI powders containing cobalt ions were obtained by suspending PANI in the following CoCl2 solutions: in H2O, in aqueous HCl, in aqueous LiCl and in acetonitrile. Thin films were prepared from a solution of PANI and CoCl2 in N-methylpyrrolidone by evaporating the solvent. Both the powders and thin films were investigated using various experimental techniques including UV/Vis, IR and XPS spectroscopies. The optimum conditions for preparation of PANI/Co powders were established and the chemical reactions taking place during the powder preparation examined. These results can be explained by consideration of the cobalt(II) species present in the reaction media. (c) 2006 Elsevier B.V. All rights reserved.