This article deals with theoretical questions raised by the consideration of health criteria in the methodology of investigation and in the validation of results in ergonomics and occupational medicine. The concept of health is redefined in the light of recent developments in the physiology of regulations, clinical psychology and psychosomatic medicine. In contrast to the conventional definition adopted by the World Health Organization, ''health'' is here conceived not as a state of being, but as an ideal. ''Normality'', unlike ''health'', is proposed as a state of equilibrium between ''suffering'' and the defenses against suffering. The significance of the idea of ''defense'' can be analyzed via regulatory physiology as well as through psychology and psychosomatic medicine. The relations between health and work are most often envisaged in reference to professional somatic pathology and to professional stress. Here, the relations between health and work have been reexamined, taking into account the last twenty years' research on the psychodynamics and psychopathology of work. This approach yields a clinical description explaining why working conditions are sometimes favourable and sometimes detrimental to health; the conceptuel framework is more precise and more analytical than the theory of stress. Taking into account the dynamics between suffering and defenses in the search for a better relation between a man and his task leads to introducing criteria of validation specific to psychic and somatic functions in the evaluation of the action. These criteria are in contradiction with the criteria of fiftness of action for its productive efficiency. The contradiction between the criteria of health and those of productivity can be analyzed scientifically so that rational choices and decisions can be made. This analysis is supported by the theory of the rationality of action formulated by J. Habermas. If criteria of health in ergonomics and occupational medicine are taken into account, research procedures are affected. These effects are examined in terms of requirements for the orientations of research in these two disciplines.
