Abstract: A process comprising extracting the blood of horseshoe crabs (Limulina) into an isotonic buffer solution containing an agent which inhibits the agglutination of amebocyte, separating the amebocyte from said solution, breaking the amebocyte, and recovering Limulina lysate, which is characterized in that methyl derivatives of xanthine such as theophyline, theobromine, or caffeine, or their salts, are used as the amebocyte's agglutination-inhibiting agent is disclosed.