Objectives of this work are to study changes in the immunoreactive HTGL mass during storage under various conditions. In addition, the shelf-life of the HTGL ELISA kit was confirmed. The immunological reactivity of HTGL in PHP stored in the liquid, frozen, or lyophilized state was monitored using purified human PHP-HTGL as the standard material. Furthermore, the long-term stability of the HTGL ELISA kit was ascertained. The immunoreactive HTGL mass in the lyophilized PHP maintained its initial immunological reactivity for at least 26 months at 4 degrees C or lower. The other reagents included in the HTGL ELISA kit also have a long shelf-life when they are stored at 4 degrees C or less. HTGL in PHP was stabilized by lyophilization and can be used as the standard material for HTGL ELISA; the HTGL ELISA kit has a long shelf-life, i.e., more than two years.