All the hypotheses concerning the basic problems of schizophrenia have been disproved, challenged or simply never corroborated. We tried to find the reasons. The first step in any research seems to be the definition of its object, but there is no definition of schizophrenia. The influence of the organogenesis versus psychogenesis dispute and of the personal convictions of searchers is inevitable and very often unconscious; it is felt at all the levels of research. The interference of other personal factors is also controversial at the research team level and notably regarding the importance of the illness concerned. Bleuler spoke about “the group of schizophrenias”, but all the studies are carried out as if, behind the diversity of the clinical description there was one single and constant organic substratum. The limitations which this idea engenders are discussed. The emphasis is on the interest in studying acute beginning forms. Various etiopathogenetic hypotheses are taken into consideration when choosing methodology; it is the least limitating hypothesis which must be the deciding factor, namely that there are, in schizophrenia, some social-psychological and some organic factors, but the presence of only one factor of any kind is sufficient. The methodological conclusions are: the value of longitudinal studies compared with sectional studies, the importance of setting up homogeneous sub-groups for at least one additional datum over that of schizophrenia and the interest of repeating the tests recommended by different schools on the same subjects. For reasons of facility, most studies deal with chronic patients, and various criteria of selection are shown. Consequences of ‘institutionalization' in a mental hospital (secondary alienation) are also looked at from the point of view of the body: it seems to us that chronicity gradually changes a person into ‘another man’, biologically speaking. The peculiarities of diets in mental hospitals were at the beginning of many contradictions and mistakes in those studies; the part of other independent variables is taken into consideration; such as the level of physical activity, stress and chemical treatments. The problem of control groups for the sectional studies is shown. Throughout the text, examples are given of repercussions on some studies of the methodological problems raised.
