Solution culture-grown, six-month old jack pine (Pinus banksiana Lamb.) seedlings were treated with naphthenic acids (NAs) (150mgl–1) and sodium chloride (45mM NaCl) which were applied together or separately to roots for four weeks. NAs aggravated the effects of NaCl in inhibiting stomatal conductance (g
s) and root hydraulic conductance (Kr). Naphthenic acids did not affect needle and root electrolyte leakage in the absence of NaCl. However, in plants treated with NaCl, NAs further increased electrolyte leakage from needles and NaCl induced electrolyte leakage from needles, but not from roots. Both NaCl and NAs treatments resulted in a reduction in root respiration. The measured Na+ and Cl– concentrations in the shoots for combined NaCl + NAs treatments were lower than in NaCl-only treatments. These decreases were correlated with a reduction in water conductance. The accumulation of Na+ and Cl– in shoots was accompanied by an increased in needle electrolyte leakage. However, greater concentrations of Cl– compared with Na+ were present in shoots and in the xylem sap suggesting that roots had relatively lower capacity for Cl– storage compared with Na+.