The adsorption of Co(II) or Ni(II) ammine complexes from aqueous solutions onto gamma-alumina at neutral or near neutral pH (7 < pH < 8.2) and ambient temperature is investigated as a function of the ion concentration in the impregnating solutions, the contact and aging times, and the drying conditions. The formation of coprecipitates including Al(III) ions extracted from the support is demonstrated by EXAFS and IR spectroscopy for contact times and Ni or Co loadings higher than 0.5 h and about 2.0 wt %, respectively. The EXAFS technique makes it possible to distinguish the Ni or Co hydroxides and basic nitrates from coprecipitates with the hydrotalcite-type structure. In other words, EXAFS is shown to be sensitive to the presence of aluminum in the coprecipitates. Furthermore, in most cases, the M(II)/Al(III) ratio (M = Ni or Co) in the supported coprecipitates can be estimated. Infrared spectroscopy can also be used as a fingerprint of coprecipitate formation through lattice octahedral modes characteristic of the NiAl and CoAl hydrotalcite-type compounds in the 400-450 cm(-1) region. Thus, alumina should not be considered systematically as inert even at pH values close to its isoelectric point. Possible mechanisms responsible for the formation of coprecipitates at pH values nonaggressive for alumina are discussed. Dialysis experiments leading to the observation of hydrotalcite crystallites at a distance from alumina suggest that a dissolution-precipitation mechanism is possibly involved and that the rate of alumina dissolution is promoted by adsorbed Ni(II) or Co(II) ions.