Publisher Summary This chapter deals with liposomal immunoassay, which has several potential advantages over other immunoassays as the conventional immunoassays use a reagent in which an antigen or antibody is chemically attached to either a single or a few molecules of the label and are often enzymes, dyes, or fluorophores. However, in a liposomal immunoassay, each liposome usually contains many molecules of marker. If an antigen or antibody is attached to each liposome rather than to individual marker molecules, signal amplification may lead to improved assay sensitivity or a more rapid measurable response. Liposomes have other potential advantages, which may arise because of the unique properties of the liposomal membrane and the separation of liposomes' contents from the surrounding aqueous milieu. Conventional immunoassays are heterogeneous, which means that they require a separation step. This step can be time-consuming and technically complex. Homogeneous assays that avoid the need for the separation stage are easier to automate and more applicable to point of care applications. The liposomes are first formed and covalently coated in Fab fragments from antibody raised against human albumin. When liposomes are coated with Fab fragments, complement-mediated lysis occurs only on reaction with albumin and intact anti-albumin antiserum. The degree of lysis and the resultant change in absorbance are dependent on the albumin concentration in the added samples.