ISO 16604:2004 describes a laboratory test method for measuring the resistance of materials used in protective clothing to penetration by blood-borne pathogens. This test method uses a surrogate microbe under conditions of continuous liquid contact. Protective clothing "pass/fail" determinations are based on the detection of viral penetration at a specific hydrostatic pressure using the ISO 13994 test apparatus. This test method is not always effective in testing protective clothing materials having thick, inner liners which readily absorbs the challenge fluid. This test method involves a sensitive assay procedure. Because of the length of time required to complete this test method, it might not be suitable for use as a material or protective clothing quality control or assurance procedure.