Rabbit platelets attached at a high density to flat glass were examined in a scanning electron microscope. Contours of neighbouring well-spread platelets were almost parallel to each other; overlapping of the edges of two cells were small and rare. Quantitative analysis has shown that overlappings actually observed were much smaller in area that those calculated on the basis of the assumption that platelets are randomly distributed on the substratum. Thus, contact inhibition of spreading is characteristic not only of nucleated cells but also of platelets.