The median effect equation (Chou, 1976) is developed and presented as a biologically plausible model for quantitative risk assessment. First, the biological plausibility is established; Second, necessary statistical development is accomplished; Third, the median effect equation is applied to 9 datasets (3 real from the Carcinogenic Potency Database, Gold et al., 1984, and 6 theoretical datasets) to assess the models performance and ability of fit a variety of dose-response curves; Last, the median effect model is applied to the estimation and use of the TDgg. The median effect model is compared to the multistage model (Crump et al., 1976) and the two stage model (Moolgavkar and Knudson, 1981). Underlying assumptions are compared and contrasted using data on reversibility of steps, steady state assumption and the definition of "biological plausibility". To place median effect model results in perspective, RsD (risk specific doses(10⁻¹-10⁻⁵) are calculated and compared with those of the multistage model.