We proposed a liposome immunosorbent assay (LISA) and a liposome immune lysis assay (LILA) for competitive measurement of an antigen by use of antigen-coupled liposomes encapsulating fluorescent marker carboxyfluorescein (CF) and clarified the effects of measuring conditions on the assay characteristics. With increase in the spacer length of hetero-bifunctional reagents used for cross-linking reaction, the amount of CF released from liposomes on coupling of antigen molecules with activated liposomes increased. The sensitivity in the LISA was affected by the arnount of the antigen coupled on the liposomes and the concentration of the antigen present in assay solutions. This competitive LISA could detect two orders of magnitude lower concentration than the conventional ELISA and could measure over five orders of the antigen concentration. Since the competitive LISA required only one washing step for B/F separation, it was useful for rapid and easy measurement of antigen with high sensitivity. By competitive LILA using antigen-coupled liposomes, the concentration of antigen could be measured successfully, though the minimal detectable antigen concentration by the competitive LILA was higher than that by ELISA.