Antibody-coupled liposomes encapsulating horseradish peroxidase (HRP) were used in liposome immunosorbent assay (LISA) to obtain the high sensitivity and signal intensity. A color development system without lysis of liposomes was proposed. By increasing the diameter of liposomes, it was possible to encapsulate a large amount of HRP into the inner water phase, and the high sensitivity was obtained by use of large unilamellar vesicles bound with many molecules of antibody. Compared with enzyme-linked immunosorbent assay (ELISA), LISA showed higher signal intensities and could measure samples of about two-order lower concentrations. Thus, LISA can be a useful immunoassay system in low concentration ranges.