Limulus Factor C is a potent antagonist of endotoxin from Gram-negative bacteria. A fusion construct containing full length Factor C has been cloned into Spodoptera frugiperda Sf9 cell. Stable Sf9 cell transfectants were obtained using Zeocin selection for 2 weeks. The recombinant Factor C (rFC) was secreted into the culture medium at 9 mg l(-1). Both the crude and partially purified rFC were able to detect lipid A at 10 pg ml(-1) in an ELISA-based lipid A binding assay.