The nitrate reductase (NR) activity and chlorophyll content were determined in two lettuce cultivars grown in three crop systems: hydroponics (floating root system), organics and traditional. Data were analyzed through randomized complete block design with a factorial arrangement (system × cultivar). The NR activity was expressed as μM of NO2- formed (g fresh weight h-1). Greater NR activity was observed in the plants grown in the hydroponics (0.0234 μM NO2- g-1 fresh weight h-1) than in the organics and traditional systems (0.0149 and 0.0120 μM NO2- g-1 fresh weight h-1 respectively). Also the total chlorophyll content was greater in the lettuce plants grown hydroponically than in the plants grown traditionally and organically (0.00144, 0.00104 and 0.00072 mg g-1 fresh weight h-1, respectively). Yield was greater in the lettuces grown hydroponically (220.75 g plant-1) than organically (44.50 g plant-1) and traditionally grown (63.50 g plant-1). During the crop cycle (90 days), two harvests of lettuce were obtained in floating root system and only one harvest in the traditional and organics culture. The lettuce culture through hydroponics showed greater NR activity and chlorophyll content and for this reason it can be a good alternative to produce lettuce with low nitrate content.