Magnesium deficiency, prostacyclin deficiency and reduced prostacyclin sensibility of the thrombocytes may possibly play an important pathophysiological role in gestosis/pre-eclampsia. For this reason, we studied the influence of magnesium sulphate (in vitro 2-16 mVal/l) on thromboelastogram, spontaneous and ADP-induced thrombocyte aggregation, prostacyclin sensitivity of the thrombocytes and prostacyclin liberation from umbilical cord vessel preparations. The thromboelastogram showed an inhibitory influence of magnesium sulphate on all measurement parameters. Spontaneous and ADP-induced thrombocyte aggregation were inhibited to a statistically significant extent. The prostacyclin sensibility of the thrombocytes was increased by magnesium-sulphate. Magnesium sulphate enhanced prostacyclin liberation from the vascular wall significantly by 20-36%. It is possible that in gestosis magnesium sulphate may exercise a favourable influence on the disturbed balance between prostacyclin production and prostacyclin sensibility of the thrombocytes by exercising an influence on coagulation, thrombocyte function and prostacyclin liberation, and that it can thus contribute towards stabilising coagulation disturbances.