The morphology of the globule leukocyte (GL) has been investigated by light and electron microscopy in normal (decidua of mouse placenta) and pathologically altered tissues (tumors of epidermis and mucous membrane in men). The results make it probable that the GL my originate from mast cells as well as from eosinophil granulocytes. The high content of basic proteins within the globules of GL has been interpreted as a nutritive function by this cell type to the surrounding tissue.