Abstract: A fluid loss test can be performed using a housing having a substantially cylindrical core disposed therein and having a cage paddle structure disposed therein substantially coaxially around the core thereby permitting continuous agitation and even fluid shear rates to be maintained during test periods. The core has an axial opening defined therein through which lost fluid permeating the core can be collected. The core is secured in the housing so that reverse flow permeability tests can be conducted thereon. Although secured in the housing during tests, the core is removable therefrom so that filter cakes applied to the core can be analyzed. The housing is maintained within a system which permits successive fluids to be introduced into the housing while maintaining substantially constant system pressure. Additionally, measured volumes of fluid can be introduced into the housing.