The control of NF-kappaB activation is a proven therapeutic strategy in the treatment of multiple inflammatory disorders. Drug discovery and development for such a therapy demands a battery of assays to reliably demonstrate both clinical effectiveness and biological safety of prospective medications. Unlike traditional in vitro biochemical analyses, cell-based assays more closely mimic the actual in vivo physiologic environment, addressing simultaneously biological activity and toxicity issues. A novel assay system, based solely on the drug resistance of a genetically engineered cell line, has been developed to provide rapid quantitative evaluation of the (anti)-inflammatory potential of test substances. The assay principle is based on the ability of bona fide inflammatory agents to activate the transcription factor NF-kappaB in cultured cells. In our model, expression of a dual drug resistance marker, driven by an NF-kappaB-dependent minimal promoter, provides a selective and highly sensitive scheme with a quantitative readout to detect biochemical agents with pro-or anti-inflammatory properties. The novel cell-based system is inexpensive, simple to perform (requiring only basic cell culture skills), accurate, and provides sensitivity comparable to that of the electrophoretic mobility shift assay and quantitative ELISA. In addition, the dual selection capability of the model provides a powerful tool to discover novel molecular components of the NF-kappaB signal transduction pathway.