The cholesterol and lipoid phosphorus levels in the serum and liquor' cerebrospinalis were studied in 40 patients suffering from ischaemic cerebral lesions. A chromatographic determination was also performed for eight sub-fractions of polar and neutral fats (lysolecithin, sphingomyelin, lecithin, phosphatidyl-ethanolamine, non-esterified fatty acids, cholesterol, triglyceride and cholesterol ester). Furthermore, five sub-fractions of cholesterol esters were prepared according to the degree of unsaturation in the individual fatty acids. The results were compared with a group of 25 control persons. No significant changes in the lipide sub-fractions were found in the serum. Total cholesterol was lower for cerebral haemorrhages, lipoid phosphorus was higher. In the liquor, no increase was found in total lipides but only a shift in some lipide fractions, the most pronounced being a lowering in triglyceride and an increase in free cholesterol and sphingomyelin. It would seem that a determination of lipides in the serum and liquor is not decisive for the diagnosis of acute vascular cerebral haemorrhages. These questions require thorough research and experimentation.