Rats were continuously exposed to vapors of xylene (320 ppm) for 30 or 90 days, other groups were exposed to toluene (320 ppm) for 30 days. After termination of exposure, different brain regions were removed for the determination of their lipid contents and ethanolamine phosphoglyceride fatty acid patterns. The 2 solvents had different effects on the animals. Xylene exposure resulted in limited transient changes. After 30 days exposure an increase in the liver to body weight ratio and a decrease in linoleic acid of ethanolamine phosphoglyceride in the cerebral cortex were observed. These changes were normalized after 90 days exposure. Toluene exposure, on the other hand, resulted in decreased weights of the body, of the brain as a whole and of the cerebral cortex. Liver weights were unchanged. Total phospholipids were found to be reduced in the cerebral cortex where also a slight increase in phosphatidic acid was observed. In this brain region a minor fatty acid of ethanolamine phosphoglyceride, 22:5 (n-3), was decreased. No changes were observed in the brainstem. The data on brain weights and lipid composition after exposure to toluene indicates a breakdown of phospholipids resulting in a loss of gray matter. The mechanism for these changes is uncertain but may involve degradation of phospholipids by phospholipase D. The effective metabolism of xylene and toluene seem to protect from fatty acid changes of brain phospholipids previously observed after exposure to chlorinated ethylenes.