Ph.D. (Psychology) / In this study the illness behavior of people with a life threatening illness was described and the relationship between stress, affect and illness behavior investigated. An overview of the literature shows that the illness behavior patients exhibit is and should be an important consideration in the diagnosis of illness and treatment of patients. This is evident in reports of a high amount of ill people who do not receive treatment and the high amount of patients who seek treatment for minor ailments. It is further evident in the light of findings that illness behavior does not always accurately represent the physical disfunction and that it may even be present in :t- the absence of a physical disfunction. The paucity of research on the illness behavior of specific patient groups, and of information on the relative effects of physical versus psychological factors on illness behavior, indicate a void in the literature. The present study investigates this relationship in a group of patients with a life threatening illness. In the first phase of the study 15 kidney transplant patients were compared to themselves, under normal conditions and conditions of stress, regarding affect, the experiencing of stress and the reporting of physical symptoms. In the second phase of the study 15 kidney transplant patients were compared to 15 patients with acute but minor ailments regarding the reporting of physical symptoms, affect, the experiencing of stress and the psychosocial impact of the illness.