Abstract: An immunoassay technique using an immunoreaction at a liposome membrane surface is described. Multilamellar liposomes comprised dipalmitoylphosphatidylcholine(DPPC), cholesterol(Chol) and anti-asialo-GM1(GA1) antigen in the molar ratio 1:1:0.1. Molybdate ions entrapped in the liposomes as marker ions were released from the liposomes by a complement-mediated immunoreaction, and acted as a catalyst for promoting the hydrogen peroxide-iodide ion redox reaction. The most suitable pH of the kinetic reaction and concentrations of hydrogen peroxide and sodium iodide for the determination of molybdate ion were found to be 1, 4.7 x 10^-3 and 1.0 x 10^-3M, respectively. To minimize the sample volume, a flow-injection method was adopted. The immunoreaction was carried out as follows. A mixed solution of sample anti-GA1 antibody, liposomes and complement were incubated at 37.5°C for 1 h. The resulting solution was injected into the kinetic-FIA system. The decrease in the number of iodide ions by the molybdate ion-catalyzed reaction was monitored using an iodide ion-selective electrode. The marker ion release was specific for the anti-GA1 antibody, and depended on the presence of a complement. The present method can be used to detect as low as 103 to 104 dilution of anti-GA1.