The influence of thiourea, l(-) cysteine and glycine on the mechanisms and kinetics of copper electrodeposition from aqueous solution at pH 1.00 +/- A 0.05 and 25 A degrees C was investigated using several complementary techniques. Rotating disc electrode current density measurements and the kinetic parameters calculated from KouteckA1/2aEuro"Levich analysis indicated that at 5 x 10(-3) M thiourea and l(-) cysteine addition the electro-reduction of Cu(II) was significantly inhibited. By contrast, upon similar addition of glycine, the reduction current density increased and the equilibrium potential moved towards more positive values. Microscopic imaging studies of the resulting Cu films showed that thiourea and l(-) cysteine led to fine-grained deposits, whilst glycine addition resulted in a coarser deposit. It is suggested the additives substantially altered the electron and mass transfer processes during electrodeposition. Both thiourea and l(-) cysteine appear to act by specific chemical interactions that lead to CuS co-crystallization. On the other hand, glycine is believed to act by mediating the Cu(II) to Cu(I) reduction process.