This SAE Aerospace Information Report (AIR) discusses the impact of the ISO Test Dusts@ chosen as replacement contaminants for the Arizona Test Dusts (AC Test Dusts)@ and the ISO calibration procedure ISO 11171 for automatic particle counters@ which replaces the calibration procedure ISO 4402 (1991)@ on laboratory performance of filter elements utilized in aerospace lubrication@ hydraulic and fuel systems@ and fluid cleanliness levels determined with automatic particle counters. Purpose: Since AC Test Dusts are no longer available@ ISO has chosen alternate test dusts: the ISO (SAE) Test Dusts@ as replacements for the AC Test Dusts. In addition@ ISO has also instituted a new calibration procedure@ ISO 11171@ for automatic particle counters (APCs) utilized in filter performance testing and measuring fluid cleanliness levels as a replacement for the previous calibration procedure ISO 4402 (1991) which utilized AC Fine Test Dust. This information report compares and contrasts laboratory filter element performance and fluid cleanliness levels obtained with the new test dusts and ISO 11171 calibration procedure to those obtained with the AC Test Dusts and the previous calibration procedure ISO 4402 (1991). It should be noted that none of the changes discussed in this report will impact filter element performance or fluid cleanliness in actual service conditions in the field. The changes in test dusts and automatic particle counter calibration will impact laboratory filter element performance specifications and performance requirements therein as well as fluid cleanliness level specifications and requirements set by OEMs and operators.