We have established a clonal cell line derived from rat microglia that proliferates in response to macrophage-colony stimulating factor (CSF-1). Like primary neonatal microglia, these cells (named RTMGL1) exhibit a ramified morphology, bind isolectin B4, express CD68 and are weakly positive for CD11b and MHC class II. CSF-1-dependent proliferation requires intact signal transduction through several pathways. RTMGL1 synthesize multiple cyclooxygenase (COX) products including 11- and 15-hydroxyeicosatetraenoic acid (HETE) and express COX-2. RTMGL1 synthesize 5-HETE from arachidonic acid (AA) likely via a 5-lipoxygenase (LO). Thus, RTMGL1 have morphological and histological characteristics of primary microglia and metabolize AA via both COX and LO pathways.