Peroxisome proliferator-activated receptor Î³ (PPARÎ³) is a member of the nuclear hormone receptor family of transcription factors. It is able to both activate and repress transcription, and is reported to negatively regulate macrophage function. Ligands for PPARÎ³ include anti-diabetic thiazolidinedione drugs, and various metabolites of arachidonic and linoleic acids (AA and LA). Whilst the addition of exogenous PPARÎ³-activating ligands can block the expression of proinflammatory gene products such as inducible nitric oxide synthase (iNOS), interleukin-1Î± (IL-1Î±) and IL-6 in macrophages, the source and identity of endogenous PPARÎ³ ligands are not known. A 12/15-lipoxygenase (LOX) is induced by IL-4 treatment of macrophages, and is able to metabolise AA or LA to form PPARÎ³ ligands. However, the role of this enzyme in the regulation of macrophage gene expression is not yet known. To investigate the production of PPARÎ³-activating ligands in cells of the myeloid lineage, and the role of these ligands in the regulation of gene expression.