Clinical psychiatrists face the dilemma of ‘humanism’ versus ‘reductionism’ when confronting the problem of diagnosing and classifying patients. The introduction of ‘operational’ or ‘explicit’ diagnostic criteria (ODC) should provide a middle-ground enabling the clinician to combine person-oriented approach with a more rigorous application of knowledge-based decision rules. More than a decade of world-wide experience with ODC should enable at least a preliminary evaluation of their utility and cost not only from the point of view of the clinician and researcher but also from the position of mental health care consumers. In order to maximize usefulness, the developpers and users of ODC should avoid their ‘reification’ as the ultimate standard in psychiatric diagnosis and retain an attitude of epistemological openness.