Electrical potential differences between the soil and the exuding xylem sap of detopped sunflower plants grown in potting compost were measured. The concentrations of some of the major nutrient ions in the soil water and in the xylem sap were determined, enabling the driving forces on the ions to be calculated. The anions, Cl, NO3 and SO4, appeared to be moving from the soil into the sap against the electrochemical potential gradient indicating active transport. There was also evidence that K and Na were actively transported into the xylem. These results are discussed in relation to those obtained with plants grown in water culture. They suggest that this could be a useful method for studying salt uptake by plants growing in the field.