Lipocalin-type prostaglandin D synthase (PGDS) is considered to be mainly produced in the leptomeninges and secreted into cerebrospinal fluid (CSF). We found PGDS levels in CSF of patients with normal pressure hydrocephalus (NPH) (8.99+/-2.59 microg/ml, mean+/-S.D., n=14) to be significantly lower than levels in a control (15.29+/-5.17, n=14, P<0.0001) and other dementia group (19.14+/-4.34, n=7, P=0.0003). Thus, PGDS level in CSF is a useful marker for the differential diagnosis of NPH from other diseases with dementia.