The effect of N and K nutrition on the salt tolerance of lettuce (Lactuca sativa L. cv. 'Salinas') and Chinese cabbage (Brassica campestris L., Pekinensis cv. Kazumi) was evaluated in three greenhouse experiments under a controlled aero-hydroponic system of cultivation. Three levels of KNO3 (1, 5 and 10 mM) were tested in all the experiments with rapidly circulated saline and nonsaline nutrient solutions. Two experiments, carried out between January and March 1989, with lettuce (Exp. I) and Chinese cabbage plants (Exp. III), consisted of two salinity levels, EC= 1.75 and 6.0 dS m-l, the former representing a nonsaline nutrient solution. In the third experiment with lettuce (Exp. II., conducted between March and May 1989), three saline nutrient solutions having EC levels of 4.7, 7.75 and 10.75 dS m-1 were compared to the nonsaline solution. The nutrient solutions were salinized with NaC1 and CaC12, in a 4:1 molar ratio. The highest yields of fresh weight of both crops were obtained from the 5 mM KNO 3 under both saline and non-saline conditions. The 10 mM treatment caused yield reduction in Chinese cabbage, probably due to a severe tipburn disorder. The relatively high fresh weight yield obtained at the lowest (1 raM) KNO 3 level can be explained by the positive effect of circulation velocity on nutrient uptake. The threshold salinity damage value for the vegetative yield of lettuce plants fed by 5 or 10 mM KNO 3 was approximately 5 dSm -1 and the yield decreased by 6.5% per unit dS m-1 above the threshold. No yield improvement due to the addition of KNO 3 occurred under highly saline conditions (Exp. II). The fresh weight of Chinese cabbage obtained from the 'saline' 1 and 5 mM KNO 3 treatments was approximately 15% lower than the 'non-saline'-treatment (Exp. III). Salinity increased tipburn and the effect was not altered by the addition of KNO 3 . No significant interaction between nutrition (KNO 3 level) and salinity was found. The application of salts increased the concentration of Na and C1