Medical ethics have always required patient consent as a prerequisit to therapy. The law concerning the "protection of persons accepting to be subjects in biomedical research" requires specific oral and written information to be given to all patients entering a clinic research project. New effects of the principal of "informed consent", on the physician-patient relationship, are analysed. Fifty patients with bronchial cancer were included in controlled studies from June 1989 to June 1990. These patients were asked to give their informed consent involving 5 different studies (2 Phase II studies investigating tolerance to a new treatment and 3 Phase III studies comparing a new treatment with a reference treatment). The patients were informed beforehand of the possibility of a research treatment and the legal requirement for their signature as well as to the possibilities of replacement solutions in case they refused. Detailed and adapted information concerning the different therapeutic solutions and their predictable side effects were presented before reading the informed consent statement. Of the 50 informed consent statements proposed, 49 were accepted. The principal of informed consent was favourably apprehended by the patients (active participation, notion of protection, information source, possibility of dialogue) and induced conditions of better acceptation by the patient. Nevertheless, it was more difficult to obtain statements of consent for studies comparing a new treatment with a reference treatment than for studies simply proposing a new treatment alone.