A method of immunoassay of a component to be measured in a sample containing hemoglobin, characterized by reacting the component to be measured in the sample containing hemoglobin to an antibody capable of binding the component to be measured in the presence of a bile acid derivative which is different from a bile acid derivative derived from the sample; a method of suppression of an effect of hemoglobin in the method of immunoassay of a component to be measured in a sample containing hemoglobin; and a reagent for immunoassay of a component to be measured in a sample containing hemoglobin, characterized by containing a bile acid derivative.
