TPA is a tumor marker characteristic of general cellular proliferation. High serum levels are found in patients with tumor progression. With the aim of bettering the clinical use, the authors have isolated TPA in purer form, in order to develop, in the future, a more specific immunoenzymatic method based on unlabeled antipeptide antibodies. A simple method for the isolation of small amounts of tissue polypeptide antigen (TPA) from the sera of patients suffering from neoplastic diseases is described. The procedure takes advantage of the availability of commercial anti-TPA coated beads; sera pools with high levels of antigen are allowed to react with such beads, then the antibody-antigen complex is dissociated by drastic changes of pH or molarity, and TPA recovered. Such TPA preparations contain low amounts of extraneous proteins, and thus can be utilized in immunoenzymatic tests, or in laboratory investigations.