Abstract: An enzyme immunoassay for an antigen using a solid phase, which employs (a) a biotinylated antibody in which a biotin derivative is bound to a thiol group of an Fab' fragment of an antibody, (b) an enzyme-labelled antibody, and (c) a solid phase immobilized with a substance capable of specifically reacting with the above biotin derivative selected from the group consisting of avidin, streptoavidin and a derivative thereof which is bound to the solid phase directly or via a linkage between another biotin derivative and a high molecular weight substance bound to the solid phase, or alternatively employs (a') a solid phase immobilized with a biotinylated antibody via a substance selected from the group consisting of avidin, streptoavidin and a derivative thereof wherein said substance is bound to the biotin moiety of said biotinylated antibody and is also bound to the solid phase directly or via a linkage between another biotin derivative and a high molecular weight substance bound to the solid phase, and (b') a

Abstract: A method for measuring the activity of lecithin cholesterol acyl transferase (LCAT) comprising adding a test sample (a blood serum or plasma) to a lecithin substrate solution containing a lecithin and a nonionic surfactant, incubating the mixture and then measuring the changed amount of the free cholesterol in the reaction system by an optical analysis, and the lecithin substrate solution useful therefor. The method of the present invention is useful for the clinical test for the liver function of patients and further for the diagnosis of the diseases, such as lipidosis and diabetes.