Conducting a dose-response analysis for an environmental contaminant requires a careful evaluation of most of the available data focusing on both the magnitude of the effect and the possible ranges of dose-response shapes which fit the data. This paper calculates potency values (1% response exposures) for human and animal data on cancer, non-cancer and biological effect endpoints for TCDD and finds that a reasonable estimate for 1% excess cancer would be between 1 and 50 pg/kg/day. The paper also evaluates the adequacy of linear and non-linear models for fitting these data and concludes that the assumption of a threshold dose-response is not fully supported by these data.