Experts in fields of organ transplantation have to make crucial decisions based on medical, social, moral and ethical factors. The paper describes the kidney allocation expert system KARES-CBR. Our system consists of two main components. Traditional expert system part uses rule-based knowledge. These rules contain general medical knowledge, such as blood group and antigens matching rules. Another group of rules contains decision making rules related to social and ethical information about organ transplantation. After decision making, the expert system component generates the list of medically suitable patients for the transplantation of an available organ.