In experiments on adult (90-120 days of postnatal life) female rats of our own breed (Wistar), the possible effect of lithium administered in four concecutive days (Na-salt, Fy Sigma, 100 mg/1 kg body weigth intraperitoneally) on the fatty acid spectrum in blood serum and brain cortex was examined. Fatty acids were measured as methyl esters (Baše 1978) using gas chromatography, and are expressed as percentage of the whole sum ( S = 100%). In experimental rats in blood serum as well as in brain cortex a significant increase of short and medium chain fatty acids was established (8:0, 10:0 and 12:0). Arachidonic acid in serum was significantelly reduced, as well as the docosahexaenoic acid (22:6 n-3), but eicosapentaenoic and docosapentaenoic acid increased significantelly. In brain cortex we found a significant decrease of polyunsaturated fatty acids (series n-3), caused by lower levels of 18:3, 20:5 and 22:6 acids. The results are discussed and the possibility of - lithium evoked changes in the ultrastructure of membrane lipid components of nervous elements is considered as possible.

        Key words: lithium, fatty acids, brain cortex, blood serum.