In the first part, the authors re-examined the concept of "hypothymie" described by J. Delay in 1946. "Hypothymie" is characterized by a mood disorder and particularly by an absence of mood and it is a fundamental syndrome of hebephrenia. From this syndrome "hypothymie", others signs will appear such as schizophrenic symptoms (characterized by attention disorder and formal thought disorder), paranoid symptoms or catatonic ones. Several authors, like J. Delay, had emphasized the importance of the mood disorder (an absence) in this pathology. It is the case of Kretschmer, Dide and Guiraud (who evoked the "athymhormie"), Bleuler, Kraepelin and also Stransky, Griesinger and at the beginning of the XIXth century, Haslam in England and Pinel in France. In the present time, "hypothymie" is related to some current concepts, especially the deficit forms of schizophrenia described by Carpenter and the schizophrenia type II defined by Crow. In the second part, the relationships between paranoid symptoms, depression and "hypothymie" were studied. The authors stressed the fact that there is an overlap between depressive and paranoid symptoms at the acute phase. They gave an illustration including 51 patients in an acute phase and in a stabilized one. In the acute phase, there was a negative correlation between positive symptoms and depressive symptoms in particular between conceptual disorganization, suspiciousness/persecution, positive formal thought disorder and depression (r = -0.65, p < 0.01; r = -0.57, p < 0.01; r = -0.66, p < 0.01 respectively). These correlations disappeared at discharge of the hospital and did not exist in the stabilized group.(ABSTRACT TRUNCATED AT 250 WORDS)