Abstract
Mast cells were detected in the brains of kangaroo rats, gerbils and albino rats. They were most numerous in diencephalic structures (leptomeninges, choroid plexuses, nuclei, tracts); moderately abundant in telencephalic and mesencephalic structures (leptomeninges, choroid plexuses, nuclei, tracts); and least plentiful in metencephalic and myelencephalic structures. They were not detected in the spinal cord. In all cases the mast cells were closely associated with the blood vessels in these regions.