This study concerns a series of 1022 patients from the Paris metro treated by homeopathy over several decades. It attempts to define the extent to which observational studies can be used to evaluate the medical-social impact, the theoretical validity and the effects of homeopathic therapy, an original discipline, straddling the empirical and the experimental, a meeting point between the labelled illness and the illness as it is experienced by the patient. To do this, all the information noted about each patient and all the effects occurring after each prescription must be systematically collected and classified. This then needs to be integrated into a databank and must be made available to researchers. The aim here is to determine the position of homeopathy in medicine and analyse the benefit and limits of observational studies. The method used within the RATP medical service will then be defined. Next, the patients are classified according to their geographical origin, gender, age, their consultations over time and their role in the company. Finally, the consultations are quantified: number, sex ratio, by year, by patient and by motive and type of pathology according to the CIST 2 classification.