Major concern over the chemical group of chlorodioxins has arisen since 2,3,7,8-tetrachlorodibenzo-p-dioxin with its extremely toxic and teratogenic properties has been found in widely distributed pesticides such as the herbicide 2,4,5-trichlorophenoxy acetic acid. Because of its chemical stability and lipophilic nature, 2,3,7,8-tetrachlorodibenzo-p-dioxin released into the environment has the potential of accumulation in the food chain. Mass spectrometry in its various forms has been the method of choice to detect and confirm low parts per billion of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Recently, a Consensus Forum held at the National Center for Toxicological Research amongst the various United States Government agencies (Food and Drug Administration, Environmental Protection Agency, US Department of Agriculture and National Institute of Environmental Health Sciences), eloquently demonstrated the potential, as well as the shortcomings, of the various techniques applied. In particular, the availability of a stable 13C labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin has proved to be an essential component to achieve low level quantitation. A brief review of the findings of the Consensus Forum is presented together with a detailed survey of the application of atmospheric pressure ionization mass spectrometry to TCDD analysis at the National Center for Toxicological Research/Food and Drug Administration.