Cerebrospinal rhinorrhoea is potentially serious due to the risk from infection. In patients presenting with a nasal discharge of clear fluid it is important to identify the nature of the fluid. Cerebrospinal fluid is readily identified by the presence of asialo-transferrin (tau protein). A method is presented for the identification of tau protein based upon agarose electrophoresis, followed by transfer onto cellulose nitrate membrane and immunochemical detection of transferrin. The method is reliable, sensitive and simple, and requires only basic electrophoresis apparatus.