The intracranial distribution of gamma activity has been studied by external scintillation scanning of the head after intraventricular (RISA-ventriculography) and intrathecal (RISA [radioactive iodinated blood albumin] -cisternography) injection of RISA. Examples of the diagnostic applications of these 2 methods in brain tumor, internal hydrocephalus, and cerebrospinal fluid rhinorrhea are presented. Observations on the dynamics of the cerebrospinal fluid circulation have been made after intrathecal injection of RISA in man.