The ultrastructure and adenosine diphosphate induced aggregatory respo
nse of platelets of 39 patients with essential hypertension have been
studied. Both, transmission and scanning electron microscopy showed th
e co-existence of various morphological forms of platelets suggestive
of activation. The hypertensive platelets also exhibited increased sen
sitivity to ADP induced aggregation confirming the activated state of
platelets; the degree of activation correlated well with the levels of
diastolic blood pressure.