Abstract: An agent for quantitative determination of microorganisms, which comprises(a) an antibody prepared from a strain of the same species as the species of microorganisms to be determined,(b) an insolubilized cell component of a strain which can sufficiently bind to the antibody (a) but does not release and replace to other strains which have been bound with the antibody (a), and(c) a labelled second antibody, and a method for the quantitative determination of microorganisms. The agent and method of the present invention are useful for determinating simultaneously not only a strain from which the antibody is prepared but also other strains of the same species which are contained in the test sample.

Abstract: A novel maleimidobenzoic acid N-hydroxysuccinimide ester of the formula: ##STR1## which is suitable as a binding agent for binding an enzyme and an antigen to give an enzyme-labeled antigen of the formula: ##STR2## wherein X and Y are different and are each an enzyme or an antigen, and an enzyme immuno assay using the enzyme-labeled antigen (II) and further a kit for the enzyme immuno assay which contains the enzyme-labeled antigen (II).

Abstract: A novel maleimidobenzoic acid N-hydroxysuccinimide ester of the formula: ##STR1## which is suitable as a binding agent for binding an enzyme and an antigen to give an enzyme-labeled antigen of the formula: ##STR2## wherein X and Y are different and are each an enzyme or an antigen, and an enzyme immuno assay using the enzyme-labeled antigen (II) and further a kit for the enzyme immuno assay which contains the enzyme-labeled antigen (II).