In this study, the concentration-dependent joint action of chromium (Cr) and salt (NaCl), two important environmental stressors, was examined in aquatic plants. Ceratophyllum demersum L. plants were exposed to Cr (0-10mM) for 5 days in the presence and absence of NaCl (0-500 mM). The effect of Cr, Na, and Cl accumulations on certain biological parameters (water content, ion leakage, relative growth rate, photosynthetic pigments, and protein and proline contents) was determined. Furthermore, the interactive effects of NaCl and Cr were evaluated using a mathematical model developed on the basis of the theory of probabilities. The highest Cr accumulation (0.42 mmol g(-1)) was found in plants treated with 10 mM Cr+ 125 mM NaCl. Treatment with 125 mM NaCl resulted in an increase in Cr accumulation compared with that in the control. However, 250 and 500 mM NaCl concentrations decreased Cr accumulation. Proline and water contents were not affected by increasing Cr concentration. However, NaCl did have a significant effect on any of the studied parameters. Furthermore, the interactive effects of Cr and NaCl on all studied parameters except for proline and water contents were determined. Except for photosynthetic pigments and proline content, effect of NaCl was higher than Cr on all studied parameters. The interactive effects were mostly antagonistic or additive. However, the mode of action for ion leakage was synergistic or additive. These results suggest that the coexistence of NaCl and Cr in aquatic ecosystems does not pose an additional ecological risk for aquatic plants.