A method for detecting or measuring an immunologically reactive substance through an immunological reaction with a reagent which is an antigen, an antibody, a carrier reagent sensitized by an antigen, or a carrier reagent sensitized by an antibody, wherein an immunological reaction product is produced in an aqueous reaction system by applying to the aqueous reaction system in which the reagent and the immunologically reactive substance are present a small voltage (preferably insufficient to cause electrolysis of the system) without substantially forming a pearl chain derived from the reagent, i.e. when the reagent includes a carrier three or more particles of carrier reagent are not arranged adjacent to one another in the form of a straight chain.