Disease-modifying approaches are being developed to treat Alzheimer’s Disease (AD). These are expected to slow the clinical progression of AD or delay the onset of AD. Biological markers, measured in cerebrospinal fluid (CSF) or in the periphery, may be useful adjuncts to clinical assessment methods for AD, especially when applied to these types of treatment approaches. Markers related to beta-amyloid and tau, components of AD lesions, can be quantified in CSF and show a stable and predictable pattern over time in AD. Biomarkers related to oxidation, such as isoprostanes, and to inflammation may provide information regarding mechanisms leading to neuronal damage. Biomarkers could be used during early clinical testing of drugs that affect key pathogenic steps in AD, such as amyloid production or clearance, to assess drug action and dose-response relationships. In large-scale clinical trials or in clinical practice, biomarkers that are easy to access, such as blood or urine tests, could help in evaluating effects of treatment.