A process for depositing a metal or metal alloy on at least one surface of a substrate comprising the steps of (a) providing said substrate; (b) treating the surface of said substrate with an activation solution comprising at least one source of metal ions selected from the group consisting of sources of ruthenium ions, sources of rhodium ions, sources of palladium ions, sources of osmium ions, sources of iridium ions, sources of platinum ions, sources of copper ions, sources of silver ions, sources of nickel ions, sources of cobalt ions, sources of gold ions and mixtures thereof such that at least one portion of said metal ions is being adsorbed on the surface of said substrate; (c) treating the surface of said substrate obtained from step (b) with a treatment solution comprising i) at least one additive independently selected from the group consisting of thiols, thioethers, disulphides and sulphur containing heterocycles, and ii) at least one reducing agent suitable to reduce the metal ions adsorbed on the surface of said substrate selected from the group consisting of boron based reducing agents, sources of hypophosphite ions, hydrazine, ascorbic acid, iso-ascorbic acid, sources of formaldehyde, glyoxylic acid, sources of glyoxylic acid, glycolic acid, formic acid, sugars, and salts of aforementioned acids; and (d) treating the surface obtained from step (c) of said substrate with a metallizing solution comprising a solvent and at least one source of metal ions to be deposited such that a metal or metal alloy is deposited thereon. (a) providing said substrate; (b) treating the surface of said substrate with an activation solution comprising at least one source of metal ions selected from the group consisting of sources of ruthenium ions, sources of rhodium ions, sources of palladium ions, sources of osmium ions, sources of iridium ions, sources of platinum ions, sources of copper ions, sources of silver ions, sources of nickel ions, sources of cobalt ions, sources of gold ions and mixtures thereof such that at least one portion of said metal ions is being adsorbed on the surface of said substrate; (c) treating the surface of said substrate obtained from step (b) with a treatment solution comprising i) at least one additive independently selected from the group consisting of thiols, thioethers, disulphides and sulphur containing heterocycles, and ii) at least one reducing agent suitable to reduce the metal ions adsorbed on the surface of said substrate selected from the group consisting of boron based reducing agents, sources of hypophosphite ions, hydrazine, ascorbic acid, iso-ascorbic acid, sources of formaldehyde, glyoxylic acid, sources of glyoxylic acid, glycolic acid, formic acid, sugars, and salts of aforementioned acids; and i) at least one additive independently selected from the group consisting of thiols, thioethers, disulphides and sulphur containing heterocycles, and ii) at least one reducing agent suitable to reduce the metal ions adsorbed on the surface of said substrate selected from the group consisting of boron based reducing agents, sources of hypophosphite ions, hydrazine, ascorbic acid, iso-ascorbic acid, sources of formaldehyde, glyoxylic acid, sources of glyoxylic acid, glycolic acid, formic acid, sugars, and salts of aforementioned acids; and (d) treating the surface obtained from step (c) of said substrate with a metallizing solution comprising a solvent and at least one source of metal ions to be deposited such that a metal or metal alloy is deposited thereon.