The fluid exudation fluxes of excised maize roots bathed in a variety of K2SO4 solutions have been measured, along with the ionic concentrations and osmolalities of the exudates. An apparent imbalance of inorganic ionic charge in the exudate, and a discrepancy in the total salt concentrations compared with the measured osmolalities, suggest the presence of significant amounts of organic anions in the exuded fluid. Thin-layer chromatographic methods indicate these to be mainly amino-acids and organic acids of the Kreb's cycle. Linear regression analysis shows that the exudation flux is satisfactorily described by a simple osmotic process together with a constant non-osmotic water flux of 0.43 μ1 cm-2 h-1. The osmotic permeability for the root is found to be 0.18 × 10-6 cm sec-1 atm-1. The exudation from sulphate media is contrasted with that from chloride media.