Monoclonal antibody (McAb) 3Hll against gastric cancer was grown in the mouse ascites system. To acquire a clinical grade product for cancer radioimmuno- imaging was purified by two step high performance liquid chromatography (HPLC) protocol using protein A and high-performance hydroxylapatite (HPHT). An analysis of data reported shows the two step HPLC method to be the best purification procedure. This protocol satisfies purity and immunoreactivity requirement, and provides an sample sterility, free-pyrogens, free-mycoplasma and non-specific IgG contamination. This procedure described was capable of generating large amounts of clinical grade monoc|onal antibody.