THE diffusion of oxygen in zirconium under the influence of an electric field has already been studied qualitatively1. Before beginning a further investigation of this phenomenon, it seemed worth while to find out whether a diffusion of the 'Ludwig Sorettype' occurred. If, under the influence of a temperature gradient, oxygen were indeed to diffuse preferentially in the direction of increasing or decreasing temperature, such an effect would be superimposed on the diffusion under the influence of an electric field if resistance heating were applied on the zirconium wire or sheet. The reason for this is that when the oxygen moves to the anode, the concentration of oxygen in that region rises, the electrical resistance increases locally and thus a temperature gradient develops along the wire or sheet. Darken and Oriani2 have found a thermal diffusion of carbon and nitrogen in iron under the influence of a temperature gradient. They could show that both nitrogen and carbon diffuse to the region of the highest temperature. In order to evaluate such an effect in the case of oxygen in zirconium, we tried several experimental methods. The most reproducible results were obtained in the following circumstances.