The centrosomes of NK and iNKT cells polarise right up to the contact site membrane during target cell killing. Low-power ((a) (main picture), (b) and (d)) and high-power ((a) (inset), (c), (e) and (f)) electron microscope images of thin (50 to 100 nm) lead-stained sections of iNKT cells ((a) through (c)) and NK cells ((d) through (f)) preincubated with HRP to label the endocytic pathway processed with DAB cytochemistry to reveal electron-dense reaction products in secretory lysosomes (SL) and conjugated to either primed C1R-CD1d ((a) through (c))or MHC I 722.221 ((d) through (f)) target cells (target) showing that the centrioles (black arrows) and accompanying microtubule organising centre (MTOC)-associated structures (for example, the Golgi complex (G)) of both iNKT and NK cells polarise right up to the plasma membrane in the centre of the lytic cell:target cell contact site to the side of the secretory cleft (SC) during target cell killing. Secretory lysosomes are distributed throughout the cell body in cells caught in the early stages of interaction with targets (d) but accumulate in the area surrounding the polarised centrosome as the cells prepare to kill ((e) and (f)) and are undetected in cells at late stages following release of their electron-dense content (for example, (a) through (c)). Note that polarised centrioles may be separated by some distance from the nucleus (N). Note also that small bumps and/or protrusions may appear from the cell surface opposite the polarised centrosome (for example, grey arrowheads in (b) and (c)). Bars = 1,000 nm ((a) (main image) and (d)), 500 nm ((b), (c), (e) and (f)) and 250 nm ((a), inset).