BACKGROUND: Peroxisome proliferator-activated receptors (PPARs) are a class of nuclear transcription factors that are activated by fatty acids and their derivatives. One of these, PPARgamma, regulates responsiveness to insulin in adipose cells, and PPARgamma-activating drugs such as pioglitazone are used in the treatment of type 2 diabetes. PPARgamma acts in myeloid-lineage cells, including T-cells and macrophages, to suppress their activation and their elaboration of inflammatory molecules. PPARgamma activation also suppresses the activated phenotype in microglia, suggesting that PPARgamma-activating drugs may be of benefit in chronic neuroinflammatory diseases. Some, but not all, nonsteroidal anti-inflammatory agents (indomethacin and ibuprofen in particular) also have activating effects on PPARgamma. DISCUSSION AND CONCLUSIONS: These observations suggest on the one hand a role for PPARgamma-activating drugs in the treatment of chronic neuroinflammatory diseases-as shown for a patient with secondary progressive multiple sclerosis by Pershadsingh et al. in this issue of the Journal of Neuroinflammation-and suggest on the other hand a possible explanation for confusing and contradictory results in trials of nonsteroidal anti-inflammatory agents in Alzheimer's disease.