The radioisotope cisternogram has proven itself to be a valuable diagnostic procedure during the evaluation of patients with cerebrospinal fluid (CSF) rhinorrhea. If it is not possible to define the origin of such a leak, extensive intracranial explorations may be required, which may or may not result in successful correction of the defect. As a functional examination with limited risk to the patient and minimal radiation exposure, the isotopic cisternogram can either establish a diagnosis of CSF rhinorrhea or eliminate cerebrospinal fluid as a cause for rhinorrhea. When occurring, CSF leaks can be shown by demonstrating a "path" from the cranial fossage into the nasal cavity. The present technique utilizes tampons placed in each nostril. A positive diagnosis of CSF rhinorrhea is made by finding a tampon impregnated with at least twice the radioactivity of a control tampon from the opposite nostril (in the presence of an intact septum). Conclusions indicate that a positive anterior fossa cisternogram may be the only evidence for hidden site of CSF leakage, especially when other signs are lacking.