Angiotensin-converting enzyme measures and cerebrospinal fluid total tau. Mean (standard error) in total tau across tertiles of cerebrospinal fluid (CSF) angiotensin-converting enzyme (ACE) activity and CSF ACE protein level, in the control group (A) and demented group (B). Analyses were adjusted for age and sex. Tertiles for CSF ACE activity: <121.66; 121.66 to 177.56; >177.56 relative fluorescence units. Tertiles for CSF ACE protein level: <2.95; 2.95 to 3.92; >3.92 ng/ml. **P < 0.01.