The bleeding rate as well as transport of K+, NO3− and PO4−−− within the bleeding sap of corn plants (Zea mays) has been studied in intervals after raising the nitrate concentration of the nutrient solution from 5 to 10 meq/1. Acceleration of the exudation process in response to increased nitrate supply is accomplished after a lag phase. During this lag phase L-ethionine causes a marked stimulation of bleeding sap exudation. A very close correlation (coefficient of correlation r = 0, 996) was found between bleeding rate and phosphate transport within the bleeding sap, whereas transport of K+ (r = 0, 868) and NO3− (r=0, 773) is not that closely correlated. Because phosphate is translocated to the Xylem after it has been metabolized in a series of organic phosphorous compounds it is concluded that the exudation process is primarily linked to oxidative phosphorylation in the root, which is apparently stimulated by ethionine after a lag period. Acceleration of respiratory chain phosphorylation may be brought about by increasing the amount of phosphate acceptors. © 1973, Walter de Gruyter. All rights reserved.