Many authoritative medical textbooks recommended use of glucose oxidase reagent strips to distinguish cerebrospinal fluid rhinorrhoea from clear nasal discharge following head injury. A study of 50 subjects with clear nasal and lacrimal secretions, demonstrated a large proportion of positive results for glucose (44 per cent). Thirteen secretions (26 per cent) contained glucose in a concentration within the normal range for CSF. The recommended use of glucose oxidase test strips for differentiating CSF leakage from other clear nasal secretions is therefore without foundation.