The application of 2,4–dichlorophenoxyacetic acid (2,4–D) in herbicidal concentrations to plants has resulted in a number of correlations with post-treatment physiological and biochemical changes. Whether these changes are of a secondary nature or actually involved in the basic mechanism of herbicidal action cannot always be determined at the present time. One such case is the influence of 2,4–D on the uptake of minerals from the soil. Wolf et al. demonstrated that the content of potassium was considerably lower and calcium was higher in leaves of 2,4–D treated plants than in controls, but when the analyses from the leaves were combined with those of the stems, these differences largely disappeared. They also noted that chlorine and sulfur were higher in treated plants than in controls, while phosphorus was lower in treated plants than in controls. Fang and Butts showed that the amount of phosphorus in the leaves from 2,4–D treated plants was much less than that found in the leaves of control plants, while the amount in either the stem or root from these two groups of plants showed no significant differences. These results have been confirmed by Rebstock et al. who have shown that the total amount of phosphorus in treated plants was lower than that in the control plants, while at the same time the total phosphorus content of the stem tissue from 2,4–D treated plants was higher than that of the non-treated plants. The phosphorus content of the roots was not appreciably changed from that of the non-treated plants. Rhodes et al. noted that treatment with 2–methyl–4–chlorophenoxyacetic acid (MCPA) greatly lowered the potassium content of tomato and rape plants and suggested that the possible mechanism of MCPA action might be by interference with potassium metabolism. However, in a later publication Rhodes reported no effect of MCPA on the uptake of potassium, calcium or magnesium. With the possibility existing that 2,4–D exerts its action through interference with potassium or phosphorus metabolism, the present study was undertaken to examine more closely the influence of 2,4–D on mineral uptake from the soil.