The ABC of clinical research is ethics, problems and design. Clinical research involves an ethical responsibility, as a series of faults can be made in this regard, either by negligence, misconduct (plagiarism, misrepresentation of data, etc.), conflict of interests or failure to protect patients rights. Ethical requirements in clinical research include considering the social value of the research, the scientific validity of the design and the respect for the subject under study, with a fair subject selection, a favourable risk-benefit value, an independent review and an informed consent. Regarding the problem explained, the solution can be found following two different directions: Analyzing on the one hand the possibilities of developing a basic experiment which will allow us to understand the different responses in fully controlled situations, or on the other hand we can carry out a clinical research which will allow us to answer the question following the analysis of patients or the design of a controlled clinical trial. Finally, research design requires knowing the appropriate methodology to be applied to the object of our interest. This involves several steps: the question itself, the establishment of the objective and the research design in order to get the answer.