We developed a endotoxin (lipopolysaccharide; LPS) assay using poly(ε-lysine)-immobilized cellulose beads and Limulus amebocyte lysate (LAL). This method is composed of two steps. First, endotoxins are selectively adsorbed on the beads in protein solutions, and then the adsorbed endotoxins are separated from the compound such as protein by centrifugation. Second, the endotoxins adsorbed on the beads are directly reacted with the LAL reagent by tubidimetric time assay using Toxinometer ET-2000 (Wako). This assay method could be used widely as a means of assaying LPS in solutions containing LAL-inhibiting or enhancing substances, such as protein. [DOI: 10.1380/ejssnt.2009.747]