Two species of rocket salad, Eruca vesicaria L. subsp. sativa Miller and Diplotaxis tenuifolia L. DC, were grown hydroponically in a growth chamber with two nitrogen levels (I or 8 mM N) to evaluate nitrate accumulation and nitrogen use efficiency. One ecotype of Eruca and two of Diplotaxis were used. Nitrogen (N) increased leaf production and the contribution of leaves to the total dry mass production in E. vesicaria but not in D. tenuifolia, and emphasized leaf area differences between the two species. The two species also showed differences in the inorganic anions and N content. D. tenuifolia ecotypes accumulated more NO3 than E. vesicaria (7.7 vs. 4.7 g kg(-1) Fresh mass). By increasing N concentration in the nutrient solution, NO3 content in leaves expressed on fresh mass basis increased in both species by 52%. Nitrogen use efficiency was greater in E, vesicaria than in D. tenuifolia (19.0 vs. 18.0), and decreased with increasing nitrogen in the nutrient solution ( 19.0 vs. 17.6).