A greenhouse experiment with 2-year-old pin oak seedlings (Quercus palustris Muenchh.) was conducted in sand culture to determine the effect of mode of entry of Cd on its subsequent toxicity and distribution within the plant. Cadmium, as CdCl2, was applied to 50 seedlings at 0, 0.1, 1.0, 10.0, and 100 ppm for 16 weeks either to the roots in a nutrient solution or to the shoots in an aqueous spray. Root application at all concentrations proved phytotoxic, causing chlorosis of the foliage at the lower Cd levels and necrosis at the higher levels. Seedlings treated through the roots had a foliar content of 10.8 ppm at the 1 ppm treatment, compared to 6.82 and 5.38 at the higher treatment levels. Twigs of root-treated seedlings generally contained more Cd than the foliage. Shoot applications of Cd caused no overt foliar or root symptoms even at the 100 ppm treatment. Cadmium content of the seedlings increased with each treatment increment until at the highest dosage (100 ppm) the foliage contained 191.6 ppm. In contrast to the distribution in root-treated seedlings, twigs contained less Cd than did the leaves. When the seedlings were transplanted in the following spring into clean sand and grown without further Cd treatment, foliage continued to concentrate abnormal amounts of Cd as a result of translocation of residual Cd. This was apparent in all the seedlings previously given root application of Cd, but only in the highest treatment level of the shoot-treated plants. Forest Sci. 25:328-332.