An experiment was carried out in a controlled temperature (CT) room for five weeks with tomato cvs., Moneymaker, Liberto, and Calypso, to investigate possible relationships between zinc (Zn) deficiency or toxicity and electrolyte leakage in plant leaves. The concentrations of Zn in nutrient solution were 0.01, 0.5, and 5.0 mg L, respectively. There were significant reductions in the dry matter and chlorophyll content of all three cultivars grown both at 0.01 (low) and 5 mg L (high) Zn compared to 0.5 mg L. The concentration of Zn at 0.01 mg L was not sufficient to provide for optimal plant growth, while 5 mg L in nutrient solution was detrimental to plant growth for all three cultivars. Dry matter production was generally lowest in the plants grown at low (0.01 mg L) Zn except for Moneymaker where the lowest biomass was in the high Zn treatment. Zinc concentration was increased in the leaves and roots with increasing Zn concentration in nutrient solution. Phosphorus concentration was toxic in the leaves of the plants grown at low (0.01 mg L) and was deficienct at high Zn (5 mg L). The electrolyte leakage (%) gradually increased in the plants grown at low and high Zn concentrations and these increases were greatest in the leaves of plants grown at low Zn (except for Moneymaker grown at high Zn where reduction in dry matter was less). The best results for all growth parameters tested were for the plants grown at 0.5 mg L Zn. The results of this short-term experiment show that electrolyte leakage which is relatively simple and easy to measure may be a good indicator of cultivar tolerance to Zn deficiency and toxicity.