Mental health nursing operates without a clear idea of the nature of both mind and mental. Increasingly, this lack of a defensible theoretical position has led to an increasing dependence on the concept of mind now current in biological psychiatry. But the materialist monism of biological psychiatry is itself open to doubt, particularly concerning its dependence on a priori assumptions about the nature of the relationship between mind and brain. The reductionism and objectivism inherent in this approach necessarily ignores that aspect of mind most germane to nursing, the first-person nature of the mental. An alternative is briefly sketched which stresses the mediation of behaviour by the brain, rather than viewing behaviour as causally related to brain processes. Adoption of this approach conserves nursing's focus on the subjective experience as being paramount. Nursing education should, therefore, be wary of incorporating the biological approach without a critical analysis of its suppositions and of the conception of human nature which it supports.