Immunoliposomes bearing anticancer prodrug activating enzymes (immuno-enzymosomes) are proposed for use in a two-phase approach to targeted chemotherapy of human cancer. In the first phase the tumor-specific immuno-enzymosomes are administered, and time is allowed for tumor localization and clearance from blood and other tissues. The second phase involves the administration of a nontoxic prodrug which is converted to a cytotoxic drug by the action of the tumor cell-bound immuno-enzymosomes. This approach is a modified form of antibody-directed enzyme prodrug therapy (ADEPT). This contribution briefly summarizes our current efforts to develop this new application for liposomes in cancer therapy. The enzyme β-glucuronidase (GUS), capable of activating anthracycline-prodrugs, was coupled to the external surface of immunoliposomes directed against ovarian carcinoma cells. These immuno-enzymosomes were tested in vitro for their enzymatic activity, stability, target cell binding capability and prodrug-activating capacity. The potential and limitations of the immuno-enzymosome concept are discussed.