This SAE Aerospace Recommended Practice (ARP) describes a procedure for determining the insoluble contamination level of the downstream side of filter elements. Results of this procedure represent the particulate released from the tested filter element under the prevailing conditions of the test. The results may be used for comparative evaluation of the effectiveness of various cleaning methods or the cleanliness of elements after cleaning or as received from manufacturers. Outline of Method: A representative portion of the contamination on the downstream side of the filter element under test is removed by placing the filter element in an ultrasonic bath for a set period of time and then withdrawing a sample through the filter under test into a vacuum flask. The sample is then filtered per ARP598. The insoluble contamination is thus transferred onto the surface of the membrane filter disk where it can be examined microscopically to determine the amount of contamination released from the filter element.