Centrosome polarisation reorganises the microtubule network to pass under the plasma membrane at the secretory cleft and thus directs and delivers secretory lysosomes to secretory sites. Electron microscopic images of conjugates prepared as in Figure 1 showing HRP in both secretory lysosomes (SL) and tubular endocytic recycling compartments (RE), illustrating that polarisation of the centrosome in both iNKT cells ((a) through (d)) and NK cells ((e) and (f)) during target cell (target) killing reorganises microtubules to pass under the contact site membrane (for example, white arrowheads in (a), (b) and (e)), thus allowing secretory lysosomes to be directed and delivered to the secretory cleft (SC) during minus end-directed movement along microtubules towards the centrioles (black arrows). (c) and (d) show nonconsecutive serial sections through the synapse of the same cell. Black arrowheads (for example, (a), (c), (e) and (f)) show secretory lysosomes in contact with the microtubules. White SL labelling (for example, (c), (d) and (f)) indicates secretory lysosomes docked at the contact site membrane. Grey arrow in (b) indicates a small cell surface protrusion projecting into the secretory cleft opposite the polarised centrosome. G = Golgi; N = nucleus. Bars = 500 nm.