Expert systems for the prediction of toxicity use a knowledge base of rules, collected from human experts, as the basis of their predictions. Publicly available examples include DEREK for Windows, HazardExpert, OncoLogic and the German Federal Institute for Risk Assessment's Decision Support System. Advantages of the expert system approach include the transparency of predictions, the ease with which new knowledge can be added and the potential for knowledge sharing, particularly between organisations. Practical applications within the pharmaceutical industry include their use in drug discovery, occupational hazard assessment and as supporting evidence in regulatory submissions.