The transcription factor nuclear factor kappa B (NFκB) regulates the production of a number of pro‐inflammatory mediators involved in polymorphonuclear and mononuclear cell activation. Measurement of NFκB DNA binding is used as an estimate of cellular activation and is usually measured by the DNA mobility shift assay. Results from the mobility shift assay can be difficult to quantify and do not allow discrimination of activity in different populations of cells in whole blood without prior separation. This paper describes a new flow cytometric method which allows rapid detection and quantification of DNA‐bound NFκB in white cell populations of whole blood. The technique is sensitive and allows discriminate analysis and quantification of bound NFκB in nuclei from polymorphonuclear and mononuclear cell populations in whole blood. Cytometry 29:182–186, 1997. © 1997 Wiley‐Liss, Inc.