<p>Background: Cell-free and concentrated ascites reinfusion therapy (CART) was approved by the National Insurance Scheme in 1981 in Japan and has since been used as a treatment modality for refractory ascites. Two filtration methods may be used for CART: the internal and external pressure filtration methods. However, the precise characteristics of each method are unknown.</p><p>Methods: Ascitic fluid will be obtained by puncture from patients with refractory cancerous ascites. The quantity of fluid obtained from each patient will be divided in half, and each half will be processed using either the internal or external pressure filtration method. The primary endpoint will be the time required for the transmembrane pressure to reach 500 mmHg. The secondary endpoints will be serial changes in the weight of the ascitic and filtered fluid, serial changes in the pressure at the inlet and outlet of the filter, measurement of the components of the ascitic and filtered fluid, and observation of the filter by visual inspection and light and electron microscopy.</p><p>Conclusion: This trial may clarify the characteristics of the two filtration methods.</p><p>Trial registration: UMIN000025382.</p>