As beta-2 transferrin is almost specific to the cerebrospinal fluid, its detection in rhinorrhea or otorrhea fluids demonstrates the occurrence of CSF fistula. We describe a highly sensitive method based on immunoaffinity-mediated capillary blotting for the detection of this cathodic isoform of transferrin in minute amounts (3 μl) of rhinorrhea or otorrhea fluids. Application of this method in a series of 10 patients with CSF fistula is reported.