Placebo can be defined as "a therapeutic effect, drug or non-drug, or a part of it which, in the condition being treated, objectively does not have any specific pharmacodynamic action." Even today when powerful drugs are available placebo is important and present in therapy. Effective therapeutic agents are also sometimes used as placebo, mostly inadvertently. In clinical pharmacological investigations placebos are used deliberately to discriminate the pharmacodynamic action of drugs from psychic and other factors which can influence the objective of the drug evalution. The use of placebo in therapeutic trials is justified only when no effective treatment is available or the symptom or disease is trivial. Placebo effect is especially pronounced in diseases where pain is an important symptom as well as in psychosomatic diseases. The extent of placebo reaction depends on patient's characteristics (reactors and non-reactors), drug presentation, as well as on personality and attitudes of the prescriber. Deliberate use of placebo other than in clinical therapeutic investigation is justified in mild mental depression and in situations where the diagnosis is known, no drug is necessary, but the patient's pressure to get a prescription is irresistible (?). Every doctor should cultivate the induction of placebo reaction in treatment of his patient, but not to the extent that the belief of the former in the action of an inactive medication starts.