Roots of month-old tomato plants (Lycopersicon esculentumMill.) were flooded for up to 36h. Shoots were removed just below the cotyledonary node, and the roots subjected to external pneumatic pressures ( ΔP=0.02 – 0.4MPa). Rates of resulting sap flow (Jv) from the hypocotyl stump were measured and solute content assessed. Increasing ΔPraisedJvand diluted sap osmolites. Dilution was proportional to flow in well-drained plants but less than proportional in flooded plants. Sap flow increased linearly over a ΔPrange of 0.2 –0.4MPa; the slope of this line representing hydraulic conductance (LP), an estimate of inherent root hydraulic conductivity. Flooding for 24h did not changeLPrelative to well-drained controls. Despite this similarLP,Jvat given values of ΔPwere always faster through flooded root systems. This is explained by greater osmolality of xylem sap and thus more negative osmotic potentials ( πsap) creating an additional driving force promotingJv. Overall, solute osmolality and solute delivery in flowing xylem sap increased as flooding was prolonged from 6 to 36h flooding. On arrival in the shoot, these solutes would exert a negative effect on leaf water potentials down to -0.08MPa. The extra solutes exported from roots of flooded plants compared with controls, included potassium, sulphate, protein, serine, 1-aminocyclopropane-1-carboxylic acid and sucrose. Flooding decreased the delivery of nitrate, hydrogen ions, most protein amino acids, glutamine, and abscisic acid. These changes in delivery of solutes are systemic messages passing from flooded roots to shoots. Their osmotic and physiological properties may modify shoot growth and development and have adaptive significance.