AbstractThe meningeal tissue of the brain and spinal cord of larval and juvenile adults of lampreys (Petromyzon marinus) was examined by routine electron microscopy, electron microscopic histochemistry, and electron‐probe x‐ray microanalysis to locate sites of iron deposition. A magnetometer was used for identification of ferromagnetic iron. Ferritin particles, representing ferric iron, are present in abundance within the cytoplasmic matrices and in dense bodies of meningeal cells of both the brain and spinal cord of larvae and juveniles. These round cells of the meninges also contain abundant glycogen and lipid. Small quantities of ferrous iron are associated to the latter inclusion. Aluminum deposits are present within an electrondense material of many ferritin‐containing inclusions of meningeal cells of the larval brain. Ferromagnetic material was not detected in larval and upstream‐migrant lampreys. The deposition of iron and aluminum in the meninges of lampreys may be related to physiological and environmental factors, respectively, and/or to an important interaction between the two