Tomato (Lycopersicon esculentum) cultivar, Marilyn F1, cucumber (Cucumis sativus) cultivar, Seraset F1, and pepper (Capsicum annum) cultivar, Charliston 52, were grown in sand culture for five weeks to investigate the effect of supplementary potassium sulphate applied to the root zone at high NaCl (60 mM) and high pH (8.5). Treatments were (1) nutrient solution alone (C); (2) nutrient solution+3mM KSO applied to root zone (C+K); (3) nutrient solution+60mmol NaCl (C+S); and (4) nutrient solution+60mmol NaCl+3mM KSO applied to root zone (C+S+K). Two pH levels (5.5 or 8.5) were combined with the above treatments (C, C+K, C+S, and C+S+K). Supplementary 3mM KSO was added to nutrient solution for three weeks. The plants grown at high NaCl and high pH produced less dry matter and chlorophyll compared to control while the C+S+K treatment was intermediate in response between the control and NaCl treatment for all three species tested. Reductions in both dry matter and chlorophyll concentrations were greater for pepper than tomato and cucumber. The deleterious effect of high salinity on plant growth was more striking than that of high pH. Membrane permeability increased with addition of 60mM NaCl and as the pH increased from 5.5 to 8.5. These increases were greatest for pepper. Supplementary KSO decreased membrane permeability in all three species to levels not significantly different from the control values. Water use was decreased by salinity in cucumber and tomato but increased in pepper compared to control values. At high pH (8.5) water use increased in all treatments. Supplementary K (C+S+K) resulted in water use levels that were similar to or slightly higher than in the control. Sodium (Na) concentration in plant tissues increased for all three species in the elevated NaCl and pH treatments. Concentration of K was in the deficient range in the plants grown at high NaCl and supplementary KSO application corrected this deficiency.