In health risk assessment, risk is commonly characterised by calculating a simple hazard quotient (HQ), which cannot reflect the actual distribution of exposure and health effect values. This study aimed to develop a new risk characterisation method, the overall risk probability (ORP) method based on probabilistic techniques. Exposure exceedence values were calculated to obtain an exposure exceedence curve (EEC). The area under the EEC was calculated as the ORP value to represent the risk. This method was demonstrated by a case study for two steroidal EDCs, 17 beta-estradiol (E2) and 17 alpha-ethinylestradiol (EE2) for fish in surface water. It was found that the risk probability of fish exposed to E2 (ORP, 8.1%) and EE2 (ORP, 27%) were both above the reference value of 2.5%, which was consistent with the results of HQ method. Assuming independent action of individual EDCs, a combined risk probability of 33% was obtained for the mixture effects of E2 and EE2. Our results implicated that the adverse health effects imposed by E2 and EE2 were significant for fish in surface water worldwide. (C) 2011 Elsevier B.V. All rights reserved.