Convincing evidence suggest that a plant-based diet is associated with a reduced risk of several chronic diseases, but the mechanisms for this association is not fully elucidated. The transcription factor nuclear factor kappa B (NF-kappa B) plays a critical role in cellular stress-, immune- and inflammatory responses. Also, NF-kappa B is identified as a promising therapeutic target both in cancer and chronic inflammation. We used monocytes stably transfected with a NF-kappa B-luciferase reporter construct in a screening of plant extracts for NF-kappa B modulators. Our aim was to identify dietary components which could induce basal NF-kappa B activity to produce a preconditioning effect, or inhibit induction of disease related NF-kappa B activity. When screening 34 dietary plants for their ability to induce basal NF-kappa B activity or inhibit lipopolysaccharide induced NF-kappa B activity we observed that 23 dietary plant extracts induced basal NF-kappa B activity, while 15 extracts attenuate induced NF-kappa B activation. These results indicate that dietary plants contain compounds that efficiently modulate NF-kappa B activity. We suggest dietary modulation of NF-kappa B may contribute to the observed beneficial effects of dietary plants on the risk of chronic diseases.