This chapter draws on the most important biological effects of ethylene oxide (EO), based as far as possible on their dose-response relationships, and to apply this information for purposes of hazard assessment for human exposure to EO. Scientific risk assessment is a critical component of the process in which regulatory agencies reach social judgment decisions regarding exposure to chemicals identified as potential health hazards. The basic procedure for selection of a dose-response model or models requires statistical examination of how well the model fits the experimental data. A risk assessment relating the degree of hemoglobin alkylation in EO-exposed workers and that caused by units of γ-radiation has been proposed by Ehrenberg and others. The concept of "radequivalence" has been used repeatedly for purposes of risk assessment by Ehrenberg and his colleagues in spite of serious reservations and debate regarding the validity of the approach.