Different motile blood cells behave in a different way upon spreading on the glass surface. Macrophages pass through all the stages of spreading described for fibroblasts (Vasiliev, Gelfand, 1976); granulocytes are polarized after a short staying in badly spread conditions, lymphocytes are polarized immediately after setting of the glass surface. In relation to the leading edge and the cell nucleus, centrioles in the described cell types are located differently. In macrophages they are mainly in the front or on one side of the nucleus, in granulocytes they lie within the ring-like nucleus, in lymphocytes they are strictly located behind the nucleus in the uropode. In all the cases, however, centrioles are localized in the central region of the cytoplasm. Their location does not appear to be connected with the movement direction of blood cells. The distal ends of the active centrioles are faced to the upper cell surface in the examined cells. It is suggested that the centriole can distinguish the free cell surface and the surface associated with the substrate.