The myelin-associated glycosphingolipid sulfatide in cerebrospinal fluid (CSF) was investigated in 20 patients with vascular dementia (VAD), 43 with Alzheimer's disease (AD) and 20 age-matched controls. The sulfatide concentration in the VAD group (307 +/- 118 nmol/l) was significantly (p less than 0.0001) higher than that in controls (145 +/- 86 nmol/l) and the AD group (178 +/- 79 nmol/l). Among the VAD patients, 8/20 had a significantly increased concentration of sulfatide (greater than mean + 2 S.D.), as compared with controls, while only 2/43 of the AD patients had a sulfatide concentration above this level. It is suggested that the elevated concentration of sulfatide in CSF from VAD patients reflects demyelination. Furthermore, sulfatide determinations, when combined with clinical findings, may be of diagnostic value, for discriminating between VAD and AD.