A method of assaying an activity of a lipid-modifying enzyme, the method comprising: (i) contacting a lipid-modifying enzyme selected from a phosphoinositide kinase, a phosphoinositide phosphatase, a phospholipase, a lipase, a sphingomyelinase and a lipid transfer enzyme, with a lipid micelle containing a biotinylated lipid and a substrate for the lipid-modifying enzyme; (ii) providing a first substance X and a second substance Y in close proximity in distance, wherein X and Y interact to produce a signal when they are in close proximity in distance, and obtaining a signal by using an assay selected from the group consisting of an SPA(scintillation proximity assay), a FRET(fluorescence resonance energy transfer) assay, a TR-FRET(time-resolved fluorescence resonance energy transfer) assay and an Amplified Luminescent Proximity Homogenous Assay, wherein the substance X binds to the biotin residue contained in the lipid micelle, and wherein the substance Y is selected from: a radioisotope taken up into the substrate for the lipid-modifying enzyme by the lipid-modifying enzyme or released from the said substrate; or a substance which specifically binds to a substrate after modification by the lipid-modifying enzyme; or a substance which specifically binds to the unmodified substrate, and wherein: when using the SPA assay, X is an SPA bead coated with the biotin-binding protein and Y is Y1, or Y2 or Y3 which is a radioisotope-labelled protein or antibody, and when using the FRET or TR-FRET assay, X comprises one of a fluorescent donor and a fluorescent acceptor and Y comprises the other thereof and Y is Y2 or Y3, and when using the Amplified Luminescent Proximity Homogenous Assay, X is a biotin-binding protein connected to one of a donor bead which releases singlet oxygen on exposure to light, and an acceptor bead which generates luminescence on contact with singlet oxygen and Y comprises the other thereof and is Y2 or Y3; and (iii) evaluating the activity of the lipid-modifying enzyme by the proximity effect signal obtained in the step (ii). (i) contacting a lipid-modifying enzyme selected from a phosphoinositide kinase, a phosphoinositide phosphatase, a phospholipase, a lipase, a sphingomyelinase and a lipid transfer enzyme, with a lipid micelle containing a biotinylated lipid and a substrate for the lipid-modifying enzyme; (ii) providing a first substance X and a second substance Y in close proximity in distance, wherein X and Y interact to produce a signal when they are in close proximity in distance, and obtaining a signal by using an assay selected from the group consisting of an SPA(scintillation proximity assay), a FRET(fluorescence resonance energy transfer) assay, a TR-FRET(time-resolved fluorescence resonance energy transfer) assay and an Amplified Luminescent Proximity Homogenous Assay, wherein the substance X binds to the biotin residue contained in the lipid micelle, and wherein the substance Y is selected from: a radioisotope taken up into the substrate for the lipid-modifying enzyme by the lipid-modifying enzyme or released from the said substrate; or a substance which specifically binds to a substrate after modification by the lipid-modifying enzyme; or a substance which specifically binds to the unmodified substrate, and wherein: when using the SPA assay, X is an SPA bead coated with the biotin-binding protein and Y is Y1, or Y2 or Y3 which is a radioisotope-labelled protein or antibody, and when using the FRET or TR-FRET assay, X comprises one of a fluorescent donor and a fluorescent acceptor and Y comprises the other thereof and Y is Y2 or Y3, and when using the Amplified Luminescent Proximity Homogenous Assay, X is a biotin-binding protein connected to one of a donor bead which releases singlet oxygen on exposure to light, and an acceptor bead which generates luminescence on contact with singlet oxygen and Y comprises the other thereof and is Y2 or Y3; and a radioisotope taken up into the substrate for the lipid-modifying enzyme by the lipid-modifying enzyme or released from the said substrate; or a substance which specifically binds to a substrate after modification by the lipid-modifying enzyme; or a substance which specifically binds to the unmodified substrate, and wherein: when using the SPA assay, X is an SPA bead coated with the biotin-binding protein and Y is Y1, or Y2 or Y3 which is a radioisotope-labelled protein or antibody, and when using the FRET or TR-FRET assay, X comprises one of a fluorescent donor and a fluorescent acceptor and Y comprises the other thereof and Y is Y2 or Y3, and when using the Amplified Luminescent Proximity Homogenous Assay, X is a biotin-binding protein connected to one of a donor bead which releases singlet oxygen on exposure to light, and an acceptor bead which generates luminescence on contact with singlet oxygen and Y comprises the other thereof and is Y2 or Y3; and (iii) evaluating the activity of the lipid-modifying enzyme by the proximity effect signal obtained in the step (ii).