The effects of organic additives on the electrochemical and morphological deposit changes from acid tin methanesulfonate solutions are presented. In the absence of additives, tin deposition is diffusion-controlled with concomitant hydrogen gas evolution and the tin deposits are rough. Addition of polyethylene glycol suppresses hydrogen gas evolution yet has little effect on the mechanism of stannous reduction and the deposit structures. Polypropylene glycol enhances stannous reduction and produces a slightly smoother tin coating. The addition of phenolphthalein to solutions already containing the glycol additives results in a kinetically-controlled tin reduction process and a smooth matte tin deposit. (C) 2004 Elsevier Ltd. All rights reserved.