The aim of nursing research is generally agreed to be the generation of knowledge, and whilst this is a relevant aim in theory-based disciplines such as sociology, the primary concern of nursing is with practice. Using examples drawn mainly from the field of mental health, it will be argued in this paper that the application of generalizable, research-based knowledge to individual, unique, person-centred practice, the so-called 'research-based practice' advocated by the Department of Health, is one of the main causes of the theory-practice gap. It will be further suggested that nursing requires a paradigm of clinical research which focuses on the individual therapeutic encounter in order to complement the existing sociological paradigm of theoretical research which is best suited to the generation of generalizable knowledge and theory. The paper will conclude by suggesting that such a clinically based research paradigm must not only focus on the individual nurse-patient relationship, but that it must be carried out by the nurse herself. Clinical research, if it is to make a difference to practice, must therefore be practitioner-based research.