a method of assaying an endotoxin using the limulus amebocyte lysate component which comprises pretreating whole blood with nitric acid and a surfactant selected from among polyoxyethylene ethers represented by the following formula : ## str1 ## wherein n is an integer of from 8 to 40 ; or : ## str2 ## polyoxyethylene sorbitans , n - alkylglucopyranosides , sodium dodecylsulfate and lithium dodecylsulfate , which enables an efficient and accuate assay of an endotoxin .