The hydrolysis of mixed solutions of AI(III), Ga(III), Al(III), Ln(III) and Zr(IV) was studied by potenbometric, spectrophotometric and Al-27- and Ga-71-NMR techniques. For the AI-Ga system formation of GaAl12(OH)(28)(11+) species seems more probable into the pH range 4 less than or equal to pH less than or equal to 5. Afterwards, the Al-13(OH)(32)(7+) species predominate in agreement with thermodynamic data obtained by SUPERQUAD program. Both tetrahedral Ga-IV and Al-IV may coexist in solution, the interval being defined by potentiometric methods. For the Ln(III)-Al(III) systems Al-27-and La-139-NMR does not confirm the chemical interaction between the two species in solution, but the physicochemical properties of the La-Al/PILCS were different than Al/PILCS, suggesting a strong interaction in the solid state. Ce(III) and Ce(IV) ions do interact with AI(III) in solution, into the pH range 2.783.0.