A method of quantitation of human pulmonary surfactant characterized by determining the quantity of human pulmonary surfactant in the test sample according to the immunological method by use of the primary monoclonal antibodies which recognize the human pulmonary surfactant apoproteins and the labeled secondary monoclonal antibodies which recognize said apoproteins but bind to a part of the antigen which is different from the one to which the primary monoclonal antibodies bind, and a reagent kit to be used for the quantitation.