A high nitrate content is a negative quality trait in vegetables. Endive (Cichorium endiviae L.) contributes considerably to human nitrate intake in Northwestern Europe. A collection of 125 commercially available cultivars of endive were grown on nutrient solution and evaluated for genetic variation between cultivars for the nitrate concentration in expressed sap. In two subsequent experiments 23 cultivars, representing the range of nitrate levels found in the first experiment, were grown both in soil and on nutrient solution. There were significant differences between cultivars in nitrate accumulation. Cultivar ‘Vicor’ consistently had the lowest nitrate content. Averaged over all experiments the nitrate concentration in expressed sap of this cultivar was 0.7 g·l-1 (19%) lower than that of two recommended cultivars. The results indicate that there may be some possibilities to reduce the nitrate content of endive by cultivar choice or breeding. However, the chances of obtaining a substantial reduction of the nitrate content of endive seem less than in some other crops, such as lettuce. The nitrate levels of the cultivars showed interactions with experiments and growth medium. There was no correlation between the cultivar means for the concentrations of nitrate and chloride, or between the concentration of nitrate and the osmolarity of the plant sap.