A murine cell line (MMGT1) has been established after transfection of primary microglial cell cultures with a v-myc-containing plasmid. This cell line was comparable with primary microglial cells with respect to morphology, presence of acetylated low density lipoprotein receptor, non-specific esterase, CD63, major histocompatibility complex antigens and CD11, and binding for Ricinus communis agglutinin. Primary microglia as well as MMGT1 cells were negative for glial fibrillary acidic protein. Different MMGT1 strains were obtained after subcloning, two of which resembled histiocytes (F4/80 and BM-8). These cell strains, MMGT12 and 16, were able to opsonize latex beads, and could be induced by endotoxins (LPS) to secrete TNF-alpha, IL-1, IL-6, TGF-beta, and EGF. The other subclones had intermediate (MCA519, ER-MP20) or mixed macrophage characteristics and did not react to endotoxin by an increase in TNF-alpha, IL-1, and TGF-beta. Our newly established murine microglial lines may prove to be useful models to study inflammation and repair in the brain.