Recently, hepatitis B virus (HBV) reactivation has attracted attention as a complication of cancer chemo- therapy or immunosuppressive therapy. To prevent hepatitis B due to HBV reactivation, practical guide- lines were issued in 2009. The guidelines include the relevant diagnostic algorithms for HBV markers (HBsAg, anti-HBc, anti-HBs, and HBV-DNA). Nonetheless, cases of acute liver failure due to HBV reacti- vation have occurred in Japan since 2009, likely because many of the physicians prescribing anti-cancer or immunosuppressive agents have not acted in conformity with the guidelines. The reasons for this non- conformance are considered to be as follows: First, the incidence of HBV reactivation varies markedly be- tween anti-cancer or immunosuppressive agents, and many physicians are simply not aware of this risk. Second, establishing a system for assessing compliance to the guidelines is complicated because it requires integrating both prescription data and HBV marker data, and then feeding back this information to physicians. Several medical faculties have established a survey system by establishing specialist teams comprising a hepatologist, pharmacist, laboratory technician, medical information manager, and other specialists. The multidisciplinary nature of these teams means that the actions of individuals are complemented and supported by the team as a whole and problems are resolved through teamwork. The role of clinical laboratory special- ists is likely to become more important, as their commitment to teamwork means that they are highly capable of supporting the development of clinical risk management initiatives. [Review].