The placebo reaction is a widely known phenomenon but the way it develops is not fully understood. This fact has given rise to numerous misinformed opinions on this subject.More research has been done in the field of placebo analgesia, where the involvement of the endogenous opioid systems was discovered some twenty years ago. Recently there have been some new discoveries concerning the role of expectancy and drug conditioning in experimentally induced placebo analgesia.The placebo reaction is very impressive not only following drug administration, but also after surgical operations. In many cases, it is extremely difficult to decide whether a therapeutic success is due to a given medical intervention or to a placebo response. The use of placebo controlled clinical studies remains an ethically charged issue.