This paper deals with polymer metallization by the electroless process. Previous studies in the authors＇ laboratory have shown the interest of plasma surface treatments of polymers before chemical metallization and the significant role they play towards the chemisorption of a catalyst (Pd2+ ions). Three different processes are used to activate the polymer surface for electroless deposition : namely, the one-step process using a mixed SnCl2-PdCl2 solution, the conventional two-step process using SnCl2, then PdCl2, and a new simplified process (using only PdCl2), previously proposed by the authors. According to the process utilized a variable initiation time is observed before metal deposition takes place in the metallization bath. The surface phenomena occurring on the polymer during this initiation time are studied by XPS through the chemical form of palladium adsorbed on the surface and through changes in the Pd surface concentration. A reaction mechanism relative to the initiation of the metallic ion reduction is proposed.