This paper addresses the relevance of research to practice under two headings using a policy analysis perspective. Firstly, the relationship of knowledge to action is considered within the context of a piece of longitudinal research into the welfare of children in hospital. The general difficulties of research application are discussed in terms of the different problem perceptions and time scales held by the policy makers who commission research, and the researchers themselves. The example cited demonstrates a useful compromise. The practical consequences arising from the distinct epistemological premises which underpin research into the natural and social worlds of nursing are considered. Secondly, the constraints on achieving research-based action are described briefly in terms of the resources of time, manpower and funding. It is concluded that an awareness of both conceptual and practical issues is essential in order to comprehend fully the complexity of, and the necessity for, a range of research approaches to nursing issues.