Activation of astrocytes is important in the pathogenesis of a variety of diseases in the central nervous system, such as infection and neurodegeneration. We found that the bacterial chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (fMLF) induced potent migration and Ca(2+) mobilization in human astrocytoma cell lines. The effect of fMLF was pertussis toxin-sensitive, suggesting the involvement of seven transmembrane, G protein-coupled receptor(s) for fMLF. Scatchard analyses revealed that astrocytoma cell lines express both high- and low-affinity binding sites for [3H]fMLF. RT-PCR confirmed the expression of transcripts of fMLF receptors, the high-affinity FPR and the low-affinity FPRL1 by these cells. Both fMLF and F peptide, a synthetic peptide domain of HIV-1 envelope protein which specifically activates FPRL1, increased secretion of IL-6 by astrocytoma cells. Our study demonstrates for the first time that FPR and FPRL1 expressed by astrocytoma cell lines are functional, and suggests a molecular basis for the involvement of these receptors in host defense in the brain.