The effect of various prostacyclin analogues on free and phospholipid-bound fatty acids in rat brain following complete ischaemia, normobaric and hypobaric hypoxia were investigated. Both ischaemic and hypoxic conditions cause a significant rise in both unsaturated (arachidonic and docosahexaenoic) and saturated (palmitic and stearic) fatty acids. Under same conditions, a significant fall in phosphatidylinositol level in brain was observed. Prostacyclin and its analogues significantly reduce the rise of free fatty acids, as well as the decrease of phosphatidylinositol.