The perfusion of intact cat skin by a saline solution of bis(glycinato) copper(II), labelled with Cu64, has been studied in a diffusion cell. It has been shown by counting the activity that the copper(II) complex perfuses the skin and over a period of 6-7 hr reaches the isotonic saline solution underneath. After this inaugural delay period a steady rate of penetration was maintained and after 24 hr about 1 mg of the complex perfused the skin. Skin samples, taken before and after, were fixed in buffered formalin and embedded in paraffin. Five micron sections were taken, stained with rubeanic acid and counterstained with 1% Eosin Y solution. Histological examination showed that copper was present in all layers of the perfused skin. This work is relevant to the solubility of metallic copper in human sweat and to the possible therapeutic value of the "copper bracelet".