Abstract: A test cell utilizing a pressure vessel having a vertically oriented filter having 7 square inches of flow area located therein with the vessel being sufficiently deep to provide a settling chamber below the filter for weighting materials which settle out in the presence of the high temperatures. The methods presented herein provide a means for testing polymer drilling muds that yield consistent and repeatable results that can be correlated to fluid loss indices of other drilling muds. The methods involve filling the vessel with polymer mud, heating the mud to the predetermined temperature, applying pressure to the drilling mud to force it through a 7 square inch flow area filter and measuring the filtrate over a predetermined period of time to establish the flow index.